Genesyscloud_integration_action 400 error on data action deployment

Does anyone know why genesyscloud_integration_action fails with 400 Bad Request when deploying a custom data action? Provider v1.65.2, Terraform v1.9.8, Sydney region. The payload is valid JSON but the API rejects the ‘input’ schema definition. HCL snippet below.

resource "genesyscloud_integration_action" "test" {
 name = "Test Action"
 ...
}

Thanks for the help.