Express Checkout API

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Overview

Affirm Express Checkout relies on two merchant-hosted API endpoints to dynamically complete checkout within the Affirm experience:

These endpoints enable Affirm to collect customer shipping details, present valid shipping methods, calculate taxes and totals, and return finalized order details to the merchant after loan confirmation.

By offloading address collection and checkout calculation into Affirm’s hosted flow, merchants can reduce front-end checkout complexity while retaining full control over shipping logic, pricing, and tax calculations on the backend.

Shipping Options API

The Shipping Options API returns all valid shipping methods for a given cart and shipping address.

Body

Field	Type	Description
items required	object	The items in the user’s cart. See Items object for details.
shipping required	object	The shipping details. See ShippingBilling object for details.
order_id	string	Merchant identifier to reference the current checkout session. Note the merchant is still expected to give an `order_id` post-loan confirmation.
currency required	string	Three-letter ISO currency code in uppercase

Items object

Field	Type	Description
display_name required	string	The display name of the product/item.
sku required	string	The product/item SKU.
unit_price required	integer	The item price amount in USD or CAD cents.
qty	integer	The item quantity.
item_image_url	string	The item’s product image URL.
item_url	string	The item’s product description page URL.
categories	array	The categories that apply to the product/item, and the hierarchy of those category definitions. Each list in the array contains one or more comma-separated strings, with the first string being the highest-level (widest) category.

ShippingBilling object

Field	Type	Description
name	object	The customer's name. See Name object for details.
address required	object	The user's address. See Address object for details.
phoneNumber	string	The customer's phone number.
email	string	The customer's email address.

Name object

Field	Type	Description
first	string	Customer’s first name. Can contain multiple words (for middle names).
last	string	Customer's last name.
full	string	Note: This field is required if the first and last names are missing. The string must contain at least two words.

Address object

Field	Type	Description
line1 required	string	Address line 1 (e.g., street, PO Box, or company name).
line2	string	Address line 2 (e.g., apartment, suite, unit, or building).
city required	string	City, district, suburb, town, or village.
state required	string	State, county, province, or region.
zipcode required	string	ZIP or postal code.
country required	string	Two-letter country code (ISO 3166-1 alpha-2).

Checkout Totals API

The Checkout Totals API calculates the final cart total after the customer selects a shipping option.

Body

Field	Type	Description
items required	object	The items in the user’s cart. See Items object for details.
shipping required	object	The shipping details. See ShippingBilling object for details.
selected_shipping_option required	object	The chosen shipping option. See ShippingOption object for details.
order_id	string	Merchant identifier to reference the current checkout session. Note the merchant is still expected to give an `order_id` post-loan confirmation.
currency required	string	Three-letter ISO currency code in uppercase

Items object

Field	Type	Description
display_name required	string	The display name of the product/item.
sku required	string	The product/item SKU.
unit_price required	integer	The item price amount in USD or CAD cents.
qty	integer	The item quantity.
item_image_url	string	The item’s product image URL.
item_url	string	The item’s product description page URL.
categories	array	The categories that apply to the product/item, and the hierarchy of those category definitions. Each list in the array contains one or more comma-separated strings, with the first string being the highest-level (widest) category.

ShippingBilling object

Field	Type	Description
name	object	The customer's name. See Name object for details.
address required	object	The user's address. See Address object for details.
phoneNumber	string	The customer's phone number.
email	string	The customer's email address.

ShippingOption object

Field	Type	Description
shipping_id required	string	The identifier of the shipping option.
shipping_type required	string	The type of shipping method.
shipping_amount required	integer	The item price amount in USD or CAD cents.

Name object

Field	Type	Description
first	string	Customer’s first name. Can contain multiple words (for middle names).
last	string	Customer's last name.
full	string	Note: This field is required if the first and last names are missing. The string must contain at least two words.

Address object

Field	Type	Description
line1 required	string	Address line 1 (e.g., street, PO Box, or company name).
line2	string	Address line 2 (e.g., apartment, suite, unit, or building).
city required	string	City, district, suburb, town, or village.
state required	string	State, county, province, or region.
zipcode required	string	ZIP or postal code.
country required	string	Two-letter country code (ISO 3166-1 alpha-2).

Updated about 9 hours ago