Cart and checkout validation adds billing address and PO number error targets

Shopify Adds Billing Address and PO Number Validation to Cart and Checkout Functions

Shopify has expanded Cart and Checkout Validation Functions in API version 2026-04 to include billing address and purchase order number validation. The platform now exposes billingAddress and poNumber fields in the function input graph, along with new checkout field error targets.

What Changed for Developers

Developers can now validate billing addresses and PO numbers directly within validation functions, without requiring client-side UI extensions. The update enables server-side enforcement of compliance rules such as blocking orders from prohibited billing countries or requiring PO numbers for B2B transactions.

The new input graph fields provide access to billing address data and purchase order numbers during the validation process. Corresponding error targets allow functions to return specific validation errors that Shopify displays to customers at the appropriate checkout fields.

Implementation Considerations

This change shifts validation logic from the client side to the server side, improving security and reliability for compliance-critical use cases. Apps that previously relied on UI extensions for billing address or PO number validation can now implement these checks in validation functions.

Developers working with B2B stores or merchants with specific billing requirements should review the updated function input schema. The server-side validation approach prevents customers from bypassing restrictions through browser manipulation or API calls.

The feature is available starting with API version 2026-04. Existing validation functions continue to work without modification, but developers can opt into the new fields by updating their function schemas and upgrading to the latest API version.

Read the full announcement →