Integration Checklist

Use this checklist to track your progress. Each item maps to the detailed in Set up Express Checkout

Prerequisites

• Create an account in the Affirm Merchant Dashboard
• Integrate the default Affirm Checkout
• Have access to your public and private API keys
• Reach out to your Affirm Account Manager to confirm availability and for next steps on building your APIs

Step 1: Create a Unique Order Identifier

• Generate a unique, high-entropy identifier (e.g. UUID) in your backend

Step 2: Configure Affirm Express Checkout

• Set checkout_variant: "express" in the merchant property
• Set shipping_and_totals_callback_url to your server-to-server endpoint
• Set order_id to the unique identifier generated in Step 1
• Provide subtotal in metadata (item cost before tax/shipping)
• Omit shipping object and total field
• Include other standard Checkout Object attributes

Step 3: Set Up Shipping & Totals HTTP Endpoint

• Endpoint accepts order_id, currency, and shipping address
• Endpoint returns order_id, currency, subtotal, and shipping_options array with shipping_type, shipping_label, shipping_amount, tax_amount, and total per option
• Verify X-Affirm-Signature HMAC header on all incoming requests
• Serve endpoint over HTTPS (TLS 1.2+)
• Meet the 5-second response time SLA
• Handle errors by returning HTTP 422 with an errors array
• Register your callback URL hostname pattern(s) with your TAM
• Allowlist Affirm's outbound IPs in your CDN/Firewall (contact TAM for list)

Step 4: Calculate Order Total

• On checkout confirmation, call Read Checkout API (GET /api/v2/checkout/{checkout_id})
• Calculate final order total from the returned shipping details
• Call Authorize Transaction API (POST /api/v1/transactions) with checkout token and order ID
• Validate your calculated total matches the authorized loan amount
• Finalize the order, then redirect customer to success or failure page based on validation

Step 5: Add Affirm Checkout Button

• Add the pre-styled Affirm Checkout button on your website for Express Checkout