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Can't regiter SIP trunk with FDQN, it only accepts...
# support
m
Everytime I try to add a sip trunk by adding a domain for a cloud PBX, it doesn't register, it only accepts IP address.
c
Hi there, Thank you for your message. Our team is currently out of the office. We operate Monday through Friday, from 9:00 AM to 8:00 PM Pacific Standard Time (PST). We’ll get back to you as soon as possible during our normal business hours. If your message is urgent, please mark it accordingly or include “URGENT” in the subject line, and we’ll do our best to respond promptly. Warm regards, Vapi Customer Support Team
m
Looks like your SIP trunk only allows IP-based registration, not domains, which is why the PBX won’t accept it. That usually happens when DNS/SRV support isn’t enabled on the trunk or provider side. A quick fix is to use the resolved IP or place a SIP proxy in front of it. Are you sure your PBX is set up for domain-based SIP, or is it IP-only? @M.Khatib
a
Hi Vapi Support Team, We are currently configuring a SIP integration between Vapi and a New Zealand-based provider (Yaxxa) for our client. We are encountering two critical issues that are preventing the AI agent (Emma) from functioning correctly. 1. Inbound Call Rejection ("Not Allowed") When we attempt to route calls from the Yaxxa platform to our Vapi SIP URI (facedoctors-yax@sip.vapi.ai), the caller immediately receives an automated message: "The number you are trying to reach is not allowed." The Assistant is correctly assigned to the SIP number in the dashboard. Request: Could you confirm if we need to whitelist specific Gateway IPs from our provider to authorize this traffic? If so, where in the current dashboard should these Termination IPs be entered to stop the "Not Allowed" rejection? 2. Transfer to Human / "Pass Back" Failure Our workflow requires the AI agent to transfer the caller back to a New Zealand clinic number (e.g., +64 9 918 7402) via the SIP trunk to avoid traditional telephony charges. The Issue: When the transfer is triggered, the call is dropped, or we receive a "Number not allowed" error. Goal: We want to "hand back" the call to the clinic's SIP URI or PBX without the call being treated as a standard outbound PSTN call. Request: What is the correct way to configure a Transfer Tool using SIP? Should we be using a specific SIP URI format for the destination to ensure the call stays on the IP network?
m
This feels like a SIP auth/routing issue rather than the agent setup itself. The “Not allowed” message usually means Vapi isn’t recognizing or trusting the Yaxxa trunk/IP, so the inbound call gets blocked at the edge. The transfer is likely failing because it’s being treated as a normal PSTN call instead of a SIP handoff. I can help you sort this out directly, are you currently using IP whitelist or SIP credentials for the trunk on your Vapi setup? @Anthony
a
HI @User , that would be great if you could help me sort this out, I am not the technical person, and we had logged this issue with Kyle from Vapi support, although we have not heard back and tried to contact him multiple times, hence i jumped on here. If we would be able to jump on a video call and sort this out we would be very grateful? Where would i be able to confirm the using IP whitelist or SIP credentials for the trunk on our Vapi setup?
m
Yes, I can help you with this, I’ve worked a lot with Vapi plus SIP setups so I can quickly pinpoint the issue. You can check in your Vapi dashboard under the SIP trunk settings: if you see username/password it’s SIP auth, if you see allowed IPs it’s IP whitelist Both issues you’re seeing usually come from trunk authorization or transfer not being passed as a proper SIP URI. Happy to jump on a quick call and fix this with you directly, we can sort it out privately. @Anthony
a
Thank you lets jump on a quick call, i can give you my zoom link
URGENT HELP - @Vapi @User Hi Vapi Support Team, We are currently configuring a SIP integration between Vapi and a New Zealand-based provider (Yaxxa) for our client. We are encountering two critical issues that are preventing the AI agent (Emma) from functioning correctly. Inbound Call Rejection ("Not Allowed") When we attempt to route calls from the Yaxxa platform to our Vapi SIP URI (facedoctors-yax@sip.vapi.ai), the caller immediately receives an automated message: "The number you are trying to reach is not allowed." The Assistant is correctly assigned to the SIP number in the dashboard. Request: Could you confirm if we need to whitelist specific Gateway IPs from our provider to authorize this traffic? If so, where in the current dashboard should these Termination IPs be entered to stop the "Not Allowed" rejection? Transfer to Human / "Pass Back" Failure Our workflow requires the AI agent to transfer the caller back to a New Zealand clinic number (e.g., +64 9 918 7402) via the SIP trunk to avoid traditional telephony charges. The Issue: When the transfer is triggered, the call is dropped, or we receive a "Number not allowed" error. Goal: We want to "hand back" the call to the clinic's SIP URI or PBX without the call being treated as a standard outbound PSTN call. Request: What is the correct way to configure a Transfer Tool using SIP? Should we be using a specific SIP URI format for the destination to ensure the call stays on the IP network?
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