Data Action 400 via Terraform - Invalid JSON Structure

Why does this setting fail with a 400 error?
Provider v1.68.4. Region au-1.
The HCL validates but the API rejects the integration_key field.

resource "genesyscloud_data_action" "test" {
 name = "test-action"
 integration_key = "abc-123"
}

400 Bad Request: The request could not be understood by the server due to malformed syntax.