sip Trunk between our Asterisk PBX and VAPI
Hey everyone! 
I'm trying to set up a BYO SIP Trunk between VAPI and my Asterisk PBX so calls can flow both ways using my company's official DID (+971XXXXXXXX).
My Setup:
DID +971XXXXXXXX registered on Cisco CUCM
Asterisk PBX as SIP gateway
PSTN connection through our voice gateway/ISP
Created BYO SIP trunk credential in VAPI pointing to my Asterisk
What I Want to Achieve:
OUTBOUND (Primary Goal):
VAPI AI Assistant → (SIP Trunk) → My Asterisk → My Voice Gateway → ISP PSTN → Customer
Customer sees call from our DID number +971XXXXXXXX
INBOUND (Secondary Goal):
Customer → ISP PSTN → My Voice Gateway → Asterisk → (SIP Trunk) → VAPI AI Assistant
Anyone calling +971XXXXXXXX reaches the AI
Current Problem:
When VAPI tries to make outbound calls, they get queued but fail with 503 service unavailable. Zero SIP traffic reaches my Asterisk (confirmed via firewall packet capture). VAPI isn't routing calls through the configured SIP trunk to my PBX at all.
Has anyone successfully set up BYO SIP trunks where VAPI connects to your PBX (not directly to PSTN)? Am I missing something?
I'm trying to set up a BYO SIP Trunk between VAPI and my Asterisk PBX so calls can flow both ways using my company's official DID (+971XXXXXXXX).
My Setup:
DID +971XXXXXXXX registered on Cisco CUCM
Asterisk PBX as SIP gateway
PSTN connection through our voice gateway/ISP
Created BYO SIP trunk credential in VAPI pointing to my Asterisk
What I Want to Achieve:
OUTBOUND (Primary Goal):
VAPI AI Assistant → (SIP Trunk) → My Asterisk → My Voice Gateway → ISP PSTN → Customer
Customer sees call from our DID number +971XXXXXXXX
INBOUND (Secondary Goal):
Customer → ISP PSTN → My Voice Gateway → Asterisk → (SIP Trunk) → VAPI AI Assistant
Anyone calling +971XXXXXXXX reaches the AI
Current Problem:
When VAPI tries to make outbound calls, they get queued but fail with 503 service unavailable. Zero SIP traffic reaches my Asterisk (confirmed via firewall packet capture). VAPI isn't routing calls through the configured SIP trunk to my PBX at all.
Has anyone successfully set up BYO SIP trunks where VAPI connects to your PBX (not directly to PSTN)? Am I missing something?
