Hi Vapi Support/Engineering — we need an SBC-side codec offer restriction for a BYO SIP trunk. Org ID: f6c41da6-9df8-429c-bbae-18f0e815ca54 Credential ID: 7ae953f8-158b-47b0-a071-4f8fa40365ce Gateway IP: 189.84.133.111 (DirectCall, Brazil) Issue: Our Brazilian SIP provider (DirectCall) rejects outbound calls with SIP 603 if the INVITE SDP offer includes unsupported codecs. Brazilian carriers typically do not negotiate and will reject the entire INVITE when extra codecs appear. Currently offered codecs include Opus and G722, which triggers the 603 rejection. Request (SBC-side change): Please restrict the outbound SDP codec offer for this specific trunk/credential to ONLY: - G729 - PCMA (G.711 A-law) - PCMU (G.711 mu-law) And remove/avoid offering: - Opus - G722 - any other wideband codecs This is blocking 100% of outbound calls on this trunk. Once applied, please confirm and (if possible) share guidance on how we can verify via SIP trace/PCAP that only G729/PCMA/PCMU are offered. Thank you.

Got it, this is pretty common with Brazilian carriers like DirectCall. They usually won’t negotiate codecs and will reject the whole INVITE if anything extra like Opus or G722 is included. This needs to be restricted at the SBC or trunk level, not just the assistant, otherwise those codecs can still slip into the SDP. If per-credential control isn’t available yet, a codec policy limiting it to G729, PCMA, and PCMU should fix it. Are you seeing those extra codecs directly in the INVITE from Vapi, or could they be added somewhere in your own SIP chain? @Milton Neto

Hi, The issue occurs because the Brazilian SIP carrier DirectCall is rejecting outbound calls due to unsupported codecs in the SDP. To resolve this, please add the

codecRestriction

field to your BYO SIP trunk credentials and configure Jambonz to filter SDP codec offers so that only the codecs supported by the carrier are sent (typically handled via RTPengine). This ensures the SDP matches the codecs accepted by the carrier and prevents call rejections. Best regards, Oshi Raghav Customer Support Team | Vapi