UCP Split Payments Extension

Before writing code

Fetch live spec: Web-search site:ucp.dev specification payment extensions split-payments and fetch the page for the exact allowed_combinations shape and the current failure-message codes. This extension governs money movement across multiple authorizations — implement it against the live spec, not from memory.

Conceptual Architecture

Scope

Split Payments (dev.ucp.common.payment.split_payments) lets a buyer pay with multiple payment instruments in a single checkout. The canonical case is a gift card covering part of the total with a card covering the rest.

Two submission modes

• Specified-amount — the platform requests a specific contribution from an instrument.
• Open-amount — the business determines the contribution at processing time. This is what gift cards need: the balance is not known to the platform, so it asks the business to take whatever is there.

Each payment instrument gains an optional amount field, in ISO 4217 minor units.