Hi! I'm having issues with inbound calls on a BYO SIP trunk setup using DIDWW. Calls never appear in Call Logs — DIDWW confirms the SIP INVITE is being sent correctly but Vapi returns 503 Service Unavailable immediately. Assistant is assigned and credential was recreated via API today. Has anyone solved this before, or can someone from the team assist via DM?

Hi @Sonicman A 503 usually means the assistant isn’t fully registered or there’s a SIP transport/credential mismatch. Try re-registering the assistant or testing the SIP credentials with a softphone first. If it still fails, DM a team member with your assistant ID and DID so they can check the backend logs.

Hi @Sonicman this usually happens when Vapi rejects the INVITE before the call is created (so nothing shows in logs). Please double-check the SIP destination URI, transport (UDP/TCP/TLS), codec offer (PCMU/PCMA), and that DIDWW is using the latest credentials. If you can share the SIP trace/INVITE headers + Vapi response, I can help pinpoint the issue fast.

"Update: I have received a SIP trace from my provider (DIDWW). The logs show that Vapi is rejecting the INVITE with a 503 Service Unavailable and the following header: X-Reason: Multiple accounts are attempting to default route this carrier

@Sonicman The problem is that someone had already connected DIDWW to VAPI in a way that says: "I am DIDWW and no-one else shall ever be" - which of course is wrong. Basically, connecting DIDWW to VAPI is a bitch! You can connect DIDWW (and other providers as well) via Cloudonix, which will completely "virtualize" all your carriers, and make VAPI believe you have a single carrier connected. Feel free to DM me for additional information.