SIP Trunk Registration Failing with 403 Forbidden During Zendesk Migration

Voice & Telephony
1

Anyone free to help troubleshoot this SIP registration issue that popped up while we are migrating telephony from Zendesk Talk to Genesys Cloud. We are setting up a new SIP trunk to replace the existing Zendesk voice channels, but the Genesys Cloud instance is rejecting the registration with a 403 Forbidden error. The error log shows: SIP/2.0 403 Forbidden - Authentication Failed.

We have verified that the username and password match the credentials generated in the Genesys Cloud Admin console under Telephony > Trunks. The IP address of our edge device is correctly whitelisted in the trunk configuration. In Zendesk, we never had to deal with such strict SIP authentication handshakes; the setup was much more plug-and-play.

We are using the Genesys Cloud EU-West region. The SIP provider is sending the REGISTER request with the correct Authorization header, but the response indicates the credentials are invalid. Could there be a specific setting in the Genesys Cloud SIP trunk configuration that enforces stricter authentication than standard SIP implementations? We have checked the digest realm and it matches. Any insights on what might be causing this rejection would be appreciated.

Thanks for the help.

2

Make sure you verify the SIP trunk authentication credentials are correctly mapped in the Genesys Cloud administration console under Admin > Telephony > SIP Trunks. The 403 Forbidden error often stems from a mismatch between the expected digest authentication realm and the actual credentials provided by the outbound trunk. While migrating from Zendesk, it is common to overlook the specific user agent string requirements or the exact IP allow-list configurations that Genesys enforces for new connections.

Check that the trunk is not blocked by any network security groups or firewall rules on the Genesys side. You can inspect the detailed registration logs using the Telephony API to see the exact rejection reason. Refer to the official documentation for SIP trunk configuration steps here: https://developer.genesys.cloud/restapi/telephony. Ensure the authentication token or password has not expired and matches the format expected by the Genesys platform. Sometimes, simply recreating the trunk credentials resolves stale cache issues on the provider side.