WebRTC Softphone 403 via Terraform Provider

Does anyone know the correct HCL structure for deploying WebRTC softphone settings?

Running terraform apply with provider v1.12.0 results in a 403 Forbidden error on the genesyscloud_webrtc_settings resource. The service account has webrtc:config:write permissions. Manual API call via Postman works fine. Suspect a scope mapping issue in the provider wrapper.