SIP 488 Answering Media Type Not Accepted on BYOC Trunks

So I’m seeing a very odd bug with our outbound calls dropping immediately after ringing. The SIP trace shows a 488 Answering Media Type Not Accepted from the carrier. This happens on 3 of our 15 BYOC trunks in Asia/Singapore.

Environment:

  • Genesys Cloud BYOC
  • Codec: G.711 u-law
  • Carrier: Local telco provider

The inbound side works fine. Is this a codec negotiation issue in the outbound routing configuration?