Checkout+ API Integration Guide

Checkout+ is not enabled by default. To get started, reach out to support@loopreturns.com to enable it for your account.

Overview

Checkout+ is Loop’s order protection product for stores that integrate via the Checkout+ API at checkout (rather than native Loop checkout extensions). It lets you offer order protection to your customers at checkout — covering returns, shipping issues, or both — via a single API call. Your integration calls the Checkout+ API during checkout, receives eligibility and pricing information, and applies the protection charge using your platform’s native fee mechanism. When the customer completes the order, your integration pushes it to the Loop Order API with two Checkout+ data points attached to the order.

When is the Checkout+ API Integration the right fit?Checkout+ API integration is designed for merchants on WooCommerce, BigCommerce, or headless / custom platforms who want to offer order protection at checkout. If your store already uses Loop’s native checkout extensions for order protection, you typically don’t need this API integration.

How It Works

Analyze the cart — Your integration sends the customer’s cart to POST /v1/analyze. The API evaluates eligibility rules, calculates the protection price, and returns a sessionId, the resolved coverage mode[], and chargeInstructions.
Present the offer — If eligible is true, display the protection offer to the customer using the price in chargeInstructions.amount and copy that matches the modes in mode[].
Apply the charge — If the customer accepts, apply the fee to the cart using whatever native fee mechanism your platform provides. Loop does not prescribe how the fee is stored on the platform.
Report the fee and session to Loop — Once the order is created, push it to the Loop Order API with both:
- A fees[] entry for the protection charge, with fees[].accepted_offer_mode set to the mode array returned by /v1/analyze, verbatim. Loop uses this to recognize the charge as a Checkout+ acceptance and activate coverage.
- A metadata entry with key: "session_id" and value set to the sessionId returned by /v1/analyze.

Base URL

All Checkout+ endpoints are served from:

https://api.loopreturns.com/storefront/v1

Note that this is distinct from the Loop Order API base (https://api.loopreturns.com/api/v1) — both are used by a complete Checkout+ integration. The cURL and code samples in this guide always show fully-qualified URLs so you can tell which service each call targets.

Authentication

Checkout+ uses the same authentication as the rest of Loop’s APIs. Send your merchant API key in the X-Authorization header — see Authentication for how to create and manage keys, the full header contract, and the 401 response shape. /v1/analyze requires the Cart scope. A key without Cart — including the key that authenticates your Order API integration — will be rejected with 401 unauthorized. Generate a dedicated Checkout+ key from Returns Management → Tools & integrations → Developer tools in the Loop Admin and select the Cart scope.

Use a Cart-only API key for Checkout+ — never re-use a broadly-scoped key. /v1/analyze is browser-callable (see CORS), so any storefront that calls it from client-side JavaScript exposes its API key to every shopper who opens the network tab. A key scoped to Cart only keeps the blast radius minimal: a leaked credential can call /v1/analyze and nothing else — it cannot read orders, modify returns, or touch any other Loop resource. Re-using a key that also carries orders, returns, or any other scope turns a routine browser leak into a full-account incident.

CORS

The Checkout+ API is browser-callable — every response (success or error) carries the following CORS headers:

Header	Value
`Access-Control-Allow-Origin`	The request’s `Origin` (echoed verbatim), or `*` when no `Origin` was sent
`Access-Control-Allow-Methods`	`GET, POST, OPTIONS`
`Access-Control-Allow-Headers`	`Content-Type, Authorization, X-Authorization`
`Access-Control-Max-Age`	`86400` (preflight cached for 24 hours)

Browsers may issue an OPTIONS preflight before the actual request whenever you send X-Authorization or a non-simple Content-Type. Loop responds to the preflight with the headers above and a 204 No Content, no merchant API key required for the OPTIONS itself.

Calling /v1/analyze directly from the browser exposes your merchant API key to anyone who inspects the network tab. Keep the credential server-side and proxy through your own backend whenever possible.

Integration Steps

Call the Analyze endpoint

Send the customer’s cart data to POST /v1/analyze whenever the cart changes or the customer reaches checkout.At minimum, include:

platform — woocommerce, bigcommerce, custom, or another string identifying your storefront.
region — the geographic region for eligibility evaluation. Either an ISO 3166-1 alpha-2 country (e.g. "US"), an ISO 3166-2 region ("US-OH"), or a structured { country, subdivision? } object.
cart — with lines, currencyCode, subtotalAmount, totalDiscountAmount, discountedSubtotalAmount, totalTaxAmount, totalAmount, and itemCount.
deliveryGroups — required only when your merchant configuration includes shippingProtection. See Shipping Protection and Delivery Methods.

Each cart line requires id, productId, quantity, totalPrice, originalTotalPrice, and title. unitPrice is optional.Optionally include a top-level cartId (a stable identifier from your platform) or sessionId (returned by a previous /analyze call) to re-use the existing offer session instead of creating a new one. See Idempotency.

curl -X POST https://api.loopreturns.com/storefront/v1/analyze \
  -H "Content-Type: application/json" \
  -H "X-Authorization: YOUR_MERCHANT_API_KEY" \
  -d '{
    "platform": "woocommerce",
    "region": "US",
    "cartId": "cart_8c2f9e7d1a4b",
    "cart": {
      "lines": [
        {
          "id": "line_001",
          "productId": "prod_67890",
          "quantity": 2,
          "unitPrice": { "amount": 2500, "currencyCode": "USD" },
          "totalPrice": { "amount": 5000, "currencyCode": "USD" },
          "originalTotalPrice": { "amount": 5000, "currencyCode": "USD" },
          "title": "Classic T-Shirt"
        }
      ],
      "itemCount": 2,
      "subtotalAmount": 5000,
      "totalDiscountAmount": 0,
      "discountedSubtotalAmount": 5000,
      "totalTaxAmount": 400,
      "totalAmount": 5400,
      "currencyCode": "USD"
    }
  }'

Handle the response

The response tells you whether the cart is eligible and, if so, what coverage was offered and how to apply the charge.

{
  "sessionId": "lop_a1b2c3d4e5f6g7h8i9j0",
  "eligible": true,
  "reason": "eligible",
  "mode": ["returnCoverage", "shippingProtection"],
  "chargeInstructions": {
    "amount": 498,
    "currencyCode": "USD",
    "method": "fee"
  },
  "metadata": {
    "priceBreakdown": [
      { "type": "base", "amount": 298, "label": "Return coverage" },
      { "type": "base", "amount": 200, "label": "Shipping protection" }
    ],
    "pricingSubtotalUsed": 5000,
    "experimentCohort": null,
    "sessionCreated": true,
    "analysisCount": 1
  }
}

Field	What it tells you
`sessionId`	Stable identifier for this offer session. Persist it alongside your cart so subsequent `/analyze` calls can re-use the same session.
`eligible`	Whether to show the protection offer.
`reason`	Why the cart is or isn’t eligible (useful for debugging).
`mode`	A subset of `["returnCoverage", "shippingProtection"]` describing what coverage was offered. Present only when `eligible` is `true` — omitted when the cart is ineligible. Drives the customer-facing copy and is reported back on the order as `fees[].accepted_offer_mode`.
`chargeInstructions.amount`	The fee to charge, in minor currency units.
`chargeInstructions.method`	`fee` for Checkout+ API integrations. (`product_line_item` is reserved for Loop’s Shopify integration.)
`metadata.priceBreakdown`	Component-by-component breakdown of how the protection price was calculated (one entry per coverage mode). Useful for debug surfaces and support tooling.
`metadata.sessionCreated`	`true` if this call created a new session, `false` if it re-analyzed an existing one.
`metadata.analysisCount`	How many analyses this session has had, including the current one.

If eligible is false, chargeInstructions is null — do not show the offer.

Apply the charge

If the customer accepts protection, add a fee to the order using whatever native mechanism your platform provides. Loop does not prescribe the storage format — only the amount and currency need to match chargeInstructions.

Suggested mechanisms (non-normative):

WooCommerce — WC_Cart::add_fee() inside woocommerce_cart_calculate_fees.
BigCommerce — the Checkout Fees API (or an order-level fee on the Orders API).
Headless / custom — any order-level fee or surcharge supported by your commerce platform.

Convert chargeInstructions.amount from minor currency units (e.g. 498 → 4.98) when your platform expects major units.

Report the fee and session to Loop

Once the order is created on your platform, push it to the Loop Order API (or upsert it via your existing order-sync pipeline). The order payload must include both:

A fees[] entry for the protection charge, with accepted_offer_mode set to the mode array returned by /v1/analyze, verbatim — do not transform, sort, or stringify the array.
A metadata entry with key: "session_id" and value set to the sessionId returned by /v1/analyze (e.g. lop_a1b2c3d4e5f6g7h8i9j0).

The fragment below highlights only the two Checkout+-specific fields on the Create Order payload — the rest of the order shape (line items, addresses, totals, customer, etc.) is unchanged. See the Create Order reference for the full schema, headers, and authentication.

{
  "...": "standard Create Order fields — see the Create Order reference",
  "fees": [
    {
      "name": "Order protection",
      "amount": { "amount": 498, "currency_code": "USD" },
      "accepted_offer_mode": ["returnCoverage", "shippingProtection"]
    }
  ],
  "metadata": [
    { "key": "session_id", "value": "lop_a1b2c3d4e5f6g7h8i9j0" }
  ]
}

The accepted_offer_mode array tells Loop which coverage modes the customer paid for:

`accepted_offer_mode`	Coverage activated
`["returnCoverage"]`	Return coverage only
`["shippingProtection"]`	Shipping protection only
`["returnCoverage", "shippingProtection"]`	Both return coverage and shipping protection

The session_id metadata entry tells Loop which offer session this acceptance corresponds to.

Checkout+ UI Guidelines

Your checkout UI controls how the protection offer is presented to customers. Loop does not inject any UI — your integration is responsible for rendering the offer, handling customer interaction, and reflecting the charge in the cart total.

Placement

Display the protection offer after the cart summary and before payment. The offer should feel like a natural part of the checkout flow, not a popup or interstitial. Recommended placements:

Below the order summary / line items
Above the payment method section
Near shipping options (especially when mode includes shippingProtection)

Place the offer where customers are already reviewing costs. This context makes the price feel incremental rather than unexpected.

Offer Display

At minimum, the offer UI should include:

Element	Source	Example
Toggle or checkbox	Your UI	A switch or checkbox the customer can interact with
Short description	Your copy (see Coverage Descriptions below)	“Protect your order against returns and shipping issues”
Price	`chargeInstructions.amount` + `chargeInstructions.currencyCode`	”$4.98”

Format the price for display by converting from minor units (e.g., 498 → $4.98). Use currencyCode to apply the correct currency symbol and formatting for the customer’s locale.

Default State

Whether the offer is pre-selected (opt-out) or unselected (opt-in) is a business decision. Consider your audience and regional requirements:

Approach	Behavior	When to use
Opt-in (default off)	Customer actively selects protection	Conservative approach; clearer consent signal
Opt-out (default on)	Customer must deselect to decline	Higher attach rates; check regional consumer protection regulations

Some jurisdictions have regulations around pre-selected charges at checkout. Verify that your default state complies with applicable laws (e.g., EU Consumer Rights Directive, FTC guidelines).

Coverage Descriptions

The mode array in the response tells you what type of protection is being offered. Use it to tailor the description shown to the customer.

`mode` contains	What it covers	Suggested description
`["returnCoverage"]`	Returns	”Get hassle-free returns on this order”
`["shippingProtection"]`	Lost, stolen, or damaged packages	”Protect your package against loss or damage during shipping”
`["returnCoverage", "shippingProtection"]`	Returns + shipping issues	”Cover your order for easy returns and shipping protection”

These are suggestions — use language that fits your brand voice. The important thing is that the description accurately reflects every mode in the array.

Loading and Error States

Your UI should handle the time between calling the API and receiving a response, as well as failures:

State	Recommendation
Loading	Hide the offer or show a skeleton/placeholder until the API responds. Do not show stale pricing from a previous cart state.
Error / timeout	Hide the offer entirely. Do not block checkout if the Checkout+ API is unavailable.
Ineligible (`eligible: false`)	Hide the offer. Do not show a disabled or grayed-out toggle.

Checkout+ should never block the checkout flow. If the API call fails, times out, or returns an error, proceed with checkout normally — without the protection offer.

Updating on Cart Changes

Re-call POST /v1/analyze whenever the cart contents change (items added, removed, or quantities updated). Pass the same cartId (or sessionId from the first response) so you re-use the existing offer session. When the cart changes:

Call /v1/analyze with the updated cart data and the same cartId / sessionId.
Update the displayed price with the new chargeInstructions.amount.
Preserve the customer’s opt-in/opt-out selection across updates.

Eligibility Changes

If a previously eligible cart becomes ineligible after a change (e.g. an excluded product is added), the next /analyze response will return eligible: false and chargeInstructions: null. Hide the offer immediately and reset any stored opt-in state — you must not apply a fee against a stale chargeInstructions.

Mode Changes

The mode array can change between /analyze calls as the cart changes (for example, removing a non-shippable item may drop shippingProtection from the array, leaving only ["returnCoverage"]). When you detect a change in array membership, re-render the coverage description and price so the customer sees what they’re actually being offered, then re-confirm their selection if the change is material.

Accessibility

Follow standard accessibility practices for the offer UI:

Use a native <input type="checkbox"> or an ARIA-equivalent toggle.
Associate the description and price with the control using <label> or aria-labelledby.
Ensure the offer is keyboard-navigable and screen-reader friendly.
Maintain sufficient color contrast for the price and description text.

Acceptance Determination

There is no explicit acceptance or rejection API call. Loop determines acceptance from the order payload your integration sends to the Loop Order API:

Outcome	How Loop determines it
Accepted	The order arrives with a `fees[]` entry whose `accepted_offer_mode` is set, and a `session_id` metadata entry. Coverage is activated and the order is billed.
Declined	The order arrives with no protection fee (no `fees[]` entry carrying `accepted_offer_mode`). No coverage, no billing.
Not shown	`/v1/analyze` returned `eligible: false`. No offer was presented.
Abandoned	The cart was analyzed but no order was placed. No action needed.

This approach is more reliable than a label-matching heuristic because the fee classifies the acceptance (accepted_offer_mode) and the metadata pairs that acceptance with the exact offer session that priced it (session_id).

Eligibility Reasons

Every /v1/analyze response carries a reason that explains the eligibility outcome. When eligible is true, reason is always eligible. When eligible is false, reason describes the disqualifying condition — use it to debug configuration issues, understand offer-attachment gaps, and drive any merchant-facing debug tooling you build on top of Checkout+.

`reason`	Meaning	What to do
`eligible`	Cart is eligible; `mode[]` and `chargeInstructions` are populated.	Show the offer.
`configuration_missing`	No Checkout+ configuration exists for this merchant.	Reach out to support@loopreturns.com to enable Checkout+.
`configuration_invalid`	Checkout+ configuration exists but is malformed.	Contact Loop support — this is a server-side fix, not a merchant request issue.
`order_protection_disabled`	Checkout+ is disabled for this merchant.	Re-enable from the Loop admin or contact support.
`empty_cart`	Cart has no line items.	Hide the offer. Don’t call `/v1/analyze` until the cart has at least one line.
`cart_only_has_coverage_products`	Cart contains only Loop coverage products — nothing to protect.	Hide the offer.
`cart_only_has_excluded_products`	Every item in the cart matches an exclusion rule.	Hide the offer.
`cart_has_excluded_product`	At least one item matches an exclusion rule and the merchant’s configuration treats that as disqualifying.	Hide the offer.
`b2b_customer_excluded`	`customer.isB2B` is `true` and the merchant excludes B2B carts.	Hide the offer. Only occurs when you pass the optional `customer` block.
`pickup_delivery_selected`	A `deliveryGroups[].deliveryMethod` is `PICKUP` or `LOCAL_DELIVERY`.	Hide the offer. Only occurs when you pass `deliveryGroups`.
`cart_total_too_low`	Cart subtotal is below the minimum threshold configured for this merchant.	Hide the offer. May become eligible after more items are added.
`cart_too_valuable`	Cart subtotal exceeds the maximum coverage amount.	Hide the offer.
`locale_not_supported`	The customer’s locale is not in the merchant’s supported locales.	Hide the offer.
`currency_not_supported`	`cart.currencyCode` is not in the merchant’s supported currencies.	Hide the offer.
`ab_test_affects_attachment_rate_control_group`	Session was assigned to an experiment control group that suppresses the offer.	Hide the offer. Expected when you opt in to experimentation.
`rule_evaluation_error`	A merchant-configured eligibility rule threw during evaluation.	Hide the offer — do not block checkout. Report the `X-Request-Id` to Loop support if the rate is non-trivial.
`system_error`	Loop encountered an unexpected error while evaluating eligibility.	Hide the offer — do not block checkout. Safe to retry the next time the cart changes.

For every ineligible reason, chargeInstructions is null and mode is omitted from the response. Treat any reason other than eligible as “hide the offer” — never present a disabled / grayed-out toggle.

Charge Instructions

When the cart is eligible, the response includes a chargeInstructions object that tells your integration how to apply the protection charge.

Field	Description
`amount`	The fee amount in minor currency units (e.g., `498` = $4.98 USD).
`currencyCode`	ISO 4217 currency code for the charge.
`method`	The charge mechanism. `fee` for Checkout+ API integrations on WooCommerce, BigCommerce, and headless storefronts. `product_line_item` is reserved for Loop’s Shopify integration where the charge is added as a hidden coverage product.
`product`	Only present when `method` is `product_line_item`. Contains `id` and `handle` for the Shopify coverage product.

When the cart is ineligible, chargeInstructions is null.

Shipping Protection and Delivery Methods

When your merchant configuration includes shippingProtection, pass deliveryGroups on every /v1/analyze call so Loop can detect pickup or local-delivery selections that disqualify the cart from shipping coverage. If you omit deliveryGroups, Loop assumes the order is being shipped and will offer shipping protection on in-store pickup orders. Each entry in deliveryGroups carries a deliveryMethod:

`deliveryMethod`	Meaning	Effect on shipping coverage
`SHIPPING`	Standard shipped delivery	Eligible
`PICKUP`	In-store or curbside pickup	Disqualifies (`reason: pickup_delivery_selected`)
`LOCAL_DELIVERY`	Merchant-operated local delivery	Disqualifies (`reason: pickup_delivery_selected`)
`DIGITAL`	Digital / no physical fulfillment	Eligible, but typically no shipping exposure

Map your platform’s native delivery types to these generic values before sending — for example WooCommerce’s local_pickup → PICKUP, BigCommerce store pickup → PICKUP.

Merchants whose protection mode is returnCoverage only do not need to send deliveryGroups — return coverage doesn’t depend on how the order is fulfilled.

Inspecting an Existing Session

GET /v1/session/{sessionId} returns the current state of an offer session without re-analyzing the cart. Use it from any context where you have the sessionId but don’t have (or don’t want to re-send) the cart payload — for example a debug surface, an admin tool, or a downstream worker auditing offer outcomes.

cURL

curl https://api.loopreturns.com/storefront/v1/session/lop_a1b2c3d4e5f6g7h8i9j0 \
  -H "X-Authorization: YOUR_MERCHANT_API_KEY"

The response is the same shape as POST /v1/analyze — sessionId, eligible, reason, mode, chargeInstructions, metadata — with two differences:

Field	Behavior
`createdAt` / `updatedAt`	Present on `GET`, not on `POST /v1/analyze`. RFC 3339 / ATOM timestamps without milliseconds (e.g. `2026-04-23T13:25:00+00:00`) that bound the session’s lifetime.
`metadata.sessionCreated`	Omitted on `GET` (it only describes the analyze call that created or re-used the session, not the session itself).

Caveats

Sessions are merchant-scoped. A session created under one merchant API key is invisible to others — you’ll get 404 session_not_found from the wrong key.
Responses are sent with Cache-Control: private, max-age=45. A short shared cache is fine for poll loops; do not cache across merchants or longer than 45 seconds.
This endpoint is not the right way to drive checkout UI updates — always re-call POST /v1/analyze when the cart contents change so pricing reflects the latest state.

Error Handling

All error responses use a consistent envelope:

{
  "error": {
    "code": "validation_error",
    "message": "Request validation failed",
    "details": {
      "cart.currencyCode": "Required",
      "cart.totalAmount": "Expected number, received string"
    }
  }
}

HTTP Status	Error Code	Condition
400	`invalid_request`	Malformed JSON, wrong `Content-Type`, body over 1 MB, or invalid `sessionId` format
400	`validation_error`	Schema validation failure — check `error.details` for per-field errors
401	`unauthorized`	Missing or invalid API key — see Authentication
404	`not_found`	Unknown route — check the URL and HTTP method
404	`session_not_found`	Well-formed `sessionId` (or path parameter) does not exist for this merchant
405	`method_not_allowed`	Wrong HTTP method for the endpoint (e.g. `GET` on `/v1/analyze`)
429	`rate_limited`	Per-merchant rate limit exceeded — retry after the indicated period
500	`internal_error`	Unexpected server error — safe to retry once
503	`service_unavailable`	Upstream dependency (typically merchant configuration) is temporarily unavailable. Retry with backoff

Every response includes an X-Request-Id header for log correlation. Include this value when contacting support about a specific request.

Idempotency

You can re-use an existing offer session in two ways:

Method	How	When to use
`sessionId`	Pass the `sessionId` from a previous response at the top level of the request	You already have a session and want to re-analyze with updated cart data
`cartId`	Pass a stable cart identifier from your platform at the top level of the request	Your platform provides a consistent cart ID across checkout (e.g. BigCommerce’s `cart_id`) and you’d rather not persist `sessionId` separately

Either approach updates the existing analysis rather than creating a new one. The response will reflect the new pricing for the updated cart, and metadata.sessionCreated will be false with metadata.analysisCount incremented.

`sessionId` semantics

The format is fixed: ^lop_[A-Za-z0-9]{20}$ (e.g. lop_a1b2c3d4e5f6g7h8i9j0).
A request with a malformed sessionId fails with 400 invalid_request. Omit the field to let Loop generate a new session.
A well-formed sessionId that does not exist for your merchant fails with 404 session_not_found. This usually means the session was never created under this API key, was created against a different environment, or has been evicted.
When both sessionId and cartId are sent, sessionId takes precedence — Loop looks up the session directly and ignores cartId for session selection.

`cartId` vs `cart.id`

These are two different fields with different roles — easy to confuse:

Field	Where	Role
`cartId`	Top-level on the analyze request	Merchant-scoped session key. Loop indexes the cart against the offer session; subsequent `/analyze` calls with the same `cartId` re-use the same session.
`cart.id`	Inside the `cart` object	On-platform identifier, echoed verbatim and surfaced in analytics / debug output. Has no idempotency role — sending only `cart.id` will not re-use a previous session.

If you want idempotent re-analysis, you must send the value at the top level as cartId (or pass sessionId).

BigCommerce provides a stable cart_id automatically. For WooCommerce and headless platforms, use whatever stable cart identifier your platform provides, or pass back the sessionId from the initial analysis.

Debugging

Set debug: true on the request to receive a debug block on the response with eligibility, pricing, and configuration diagnostics. Use this only during integration testing — the field is gated behind the request flag and is not intended for production use. Always include the X-Request-Id from the response header when reporting issues to Loop support. It is the fastest way for us to pull the full request/response trace from our logs.

Analytics & Experimentation

/v1/analyze accepts a handful of optional fields that do not influence pricing or eligibility but help Loop segment attach-rate reporting and run A/B tests on your behalf. They’re safe to omit — pass them when you want the analytics value.

Field	Type	Purpose
`experimentationConsent`	`boolean`	Opt the session in to A/B test cohort assignment. When `true`, Loop may assign a cohort and return it in `metadata.experimentCohort`; when `false` or omitted, `metadata.experimentCohort` is always `null`. Required if you want this session to participate in Loop-run experiments.
`offerOrigin`	`string`	Where the offer is being presented — e.g. `"checkout"`, `"cart"`. Defaults to `"custom"` when omitted. Analytics only.
`mountTarget`	`string`	UI mount location — e.g. `"below_shipping"`, `"order_summary"`. Defaults to `"custom"` when omitted. Analytics only.
`cartExperience`	`string`	UI experience variant identifier — e.g. `"widget"`, `"modal"`. Defaults to `"api"` when omitted. Analytics only.

If a session is assigned to an experiment control group that suppresses the offer, /v1/analyze will return eligible: false with reason: ab_test_affects_attachment_rate_control_group. Treat this the same as any other ineligible outcome — hide the offer.

Technical Considerations

Consideration	Requirement
Monetary values	All amounts on `/v1/analyze` are in minor currency units (cents). `$10.00` = `1000`. The Order API uses major-unit decimal strings — convert when you push the fee.
Currency codes	ISO 4217 format (e.g., `USD`, `EUR`, `GBP`).
Cart updates	Re-call `/v1/analyze` whenever the cart changes to get updated pricing, passing the same `cartId` or `sessionId`.
Mode mapping	Pass `mode[]` through to `fees[].accepted_offer_mode` verbatim — do not collapse, sort, or transform the array.
Session linkage	Pass the `sessionId` from `/v1/analyze` through to the order as a `metadata` entry with `key: "session_id"`. Use the key name exactly.
Request body size	The `/v1/analyze` endpoint enforces a 1 MB request body limit. Larger payloads are rejected with `400 invalid_request` (“Request body too large”). Trim oversized cart attributes (e.g. raw HTML or base64-encoded blobs) before sending.
Additive changes	Loop may add new fields to API responses at any time. Build your integration to tolerate unknown fields.

Analyze Cart — API Reference

Full request and response schema for the POST /v1/analyze endpoint.

Create Order — API Reference

Where to push the order with fees[].accepted_offer_mode and the session_id metadata entry so Loop can activate Checkout+ coverage and link the order to its offer session.

Loop Anywhere

Push commerce data into Loop from any source — orders, products, customers, and more.

Introduction

Guides

Use Cases

Return Create

Overview

How It Works

Base URL

Authentication

CORS

Integration Steps

Checkout+ UI Guidelines

Placement

Offer Display

Default State

Coverage Descriptions

Loading and Error States

Updating on Cart Changes

Eligibility Changes

Mode Changes

Accessibility

Acceptance Determination

Eligibility Reasons

Charge Instructions

Shipping Protection and Delivery Methods

Inspecting an Existing Session

Caveats

Error Handling

Idempotency

`sessionId` semantics

`cartId` vs `cart.id`

Debugging

Analytics & Experimentation

Technical Considerations

Analyze Cart — API Reference

Create Order — API Reference

Loop Anywhere

Introduction

Guides

Use Cases

Return Create

Documentation Index

​Overview

​How It Works

​Base URL

​Authentication

​CORS

​Integration Steps

​Checkout+ UI Guidelines

​Placement

​Offer Display

​Default State

​Coverage Descriptions

​Loading and Error States

​Updating on Cart Changes

​Eligibility Changes

​Mode Changes

​Accessibility

​Acceptance Determination

​Eligibility Reasons

​Charge Instructions

​Shipping Protection and Delivery Methods

​Inspecting an Existing Session

​Caveats

​Error Handling

​Idempotency

​sessionId semantics

​cartId vs cart.id

​Debugging

​Analytics & Experimentation

​Technical Considerations

​Related Resources

Analyze Cart — API Reference

Create Order — API Reference

Loop Anywhere

Overview

How It Works

Base URL

Authentication

CORS

Integration Steps

Checkout+ UI Guidelines

Placement

Offer Display

Default State

Coverage Descriptions

Loading and Error States

Updating on Cart Changes

Eligibility Changes

Mode Changes

Accessibility

Acceptance Determination

Eligibility Reasons

Charge Instructions

Shipping Protection and Delivery Methods

Inspecting an Existing Session

Caveats

Error Handling

Idempotency

`sessionId` semantics

`cartId` vs `cart.id`

Debugging

Analytics & Experimentation

Technical Considerations

Related Resources