Hi Vapi team, I'm having trouble connecting my Vonex SIP Trunk for outbound calls. Error: Ended: Call.in progress.error providerfault outbound sip 403 forbidden Call ID example: 019e3ccd-f9c4-7554-9600-50144a4237c2 Credential ID: 8f36ec98-e3d7-49b3-b19c-65c13fff70d1 Phone Number ID: 27c31464-dd45-417d-852c-921b7715263d (or the latest one) What I already did: Configured gateways 177.53.16.6:5060 and 177.53.16.41:5060 Added username 551111118958496 + password Enabled outboundLeadingPlusEnabled and optionsPingEnabled Using Tech Prefix 874302 on destination number Confirmed with Vonex that Vapi IPs are whitelisted Calls stay in queued and then fail with 403 Forbidden. Could you help check what is causing the 403 on the Vonex trunk? Thanks in advance!

This 403 usually means Vonex is rejecting the SIP request rather than a connectivity issue. It’s often tied to auth method mismatch, From/PAI formatting, or how the tech prefix is being interpreted in their routing. I’ve also seen this happen when the trunk is expecting IP based auth instead of username/password. I can help you pinpoint it quickly do you know if Vonex has your trunk set to IP auth or digest auth, and can you share one failed SIP log? @Vinicius CSTec

Hey I can see the outbound payload prepared for your call (019e3ccd-f9c4-7554-9600-50144a4237c2): • Dialed Destination: 8743025511976197648 (Tech Prefix 874302 + country code 55 + number) • Outbound Leading Plus Status: Your credential (8f36ec98-e3d7-49b3-b19c-65c13fff70d1) is configured with "outboundLeadingPlusEnabled": true Why This Causes a 403 Forbidden Because outboundLeadingPlusEnabled is set to true, Vapi automatically prepends a + to the outbound dialed string when sending the SIP INVITE. This means the SIP request was sent to Vonex's gateways formatted as: +8743025511976197648 Carriers requiring a Tech Prefix (such as 874302) expect the prefix to be the absolute first digits in the dial string. When Vonex receives the leading + before the prefix, their SBC fails to match the prefix, causing it to reject the call with a 403 Forbidden. To resolve your issue, set outboundLeadingPlusEnabled to false on your BYO SIP Trunk credential. You can do this in your Vapi Dashboard under the Credentials section by editing your "Vonex Trunk Outbound" credential.

Guys, sorry for the delay in replying... thank you very much for the answers and I will test the solutions you proposed, and as soon as I validate them I will return here with what I achieved!!!

Sure, let us know if you need help with anything related to vapi.