A 403 error means "Forbidden" and is sent by the VoIP provider or SIP server to Bria. It means that they are understanding your registration or call request but refuse to fulfill it. This could be for a number of reasons including:
- Incorrect username/password
- Number being called is not supported (eg long-distance)
- Lack of funds in account
- Too many failed registrations
You will need to reach out to the provider to see why they are sending this error to Bria.