New rejection reason codes and merchant message added to verificationSessionReject mutation

The verificationSessionReject mutation in the Payments Apps API now supports two new rejection reason codes and an optional merchant-facing message. The new enum values on VerificationSessionStateReason include:

• RESOURCE_NOT_FOUND: The payment method could not be found in the payment provider's system.
• RESOURCE_INVALID: The payment token is not valid for this use case (for example, a mismatch between customer and payment method).

A new input field on VerificationSessionRejectionReasonInput(https://shopify.dev/docs/api/payments-apps/2026-04/input-objects/VerificationSessionRejectionReasonInput) has also been added:

• merchantMessage (string, optional): A custom, localized message to provide to the merchant when a verification is rejected.

These changes give payment apps more granular control over verification rejection reporting.