Shopify has expanded Cart and Checkout Validation Functions to support billing address and purchase order (PO) number validation as of API version 2026-04. Developers can now access billingAddress and poNumber fields directly in the function input graph and leverage new checkout field targets to enforce validation rules server-side, eliminating the need for client-side workarounds.
This update significantly strengthens backend validation capabilities for merchants with complex compliance requirements. B2B merchants can now require PO numbers at checkout, while any store can enforce billing restrictions—such as blocking prohibited countries—directly through validation functions rather than relying on UI extensions or post-purchase manual reviews. This server-side approach is more secure, consistent, and reduces cart abandonment from validation errors.
GetShopifyToken makes it easy to authenticate and manage your Shopify API access with the latest API versions. With streamlined token generation, you can quickly start implementing these new validation features in your Cart and Checkout Functions.