Genesyscloud_integration_action 422 on Data Action deploy

Terraform v1.9.8
Provider v1.65.2
Region: Australia/Sydney

Deploying custom data action via genesyscloud_integration_action.
HCL defines payload structure.

Apply fails with 422 Unprocessable Entity.
Error: invalid schema for action definition.

Payload validated against OpenAPI spec. Works via Postman.

Why does this setting cause 422 error in Terraform but not in direct API call?