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Call Transfer failing with custom telephony provid...
# ❓・bug-report
a
Multiple of our users have been experiencing failing call transfers. We're using Telnyx as a custom telephony provider. Error received:
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2026-01-14 00:32:54.449 call_0eeb9a8ec391e6dab96dfa3a575 error: Error transferring call, SIP status code: 403 SIP error category: telephony_provider_permission_denied Error: twirp error unknown: unexpected status from INVITE response: sip status: 403: Unverified origination number D51
Call ids:
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call_0eeb9a8ec391e6dab96dfa3a575
call_9da92964107939119d5d2a8d932
o
Hello @Andreas , did you add the X-Telnyx-Username header to the INVITE ?
a
is that the username field when importing the number on Retell?
o
a
We're using SIP connection on Telnyx, other than that I don't believe we have access to modify INVITE headers?
The outage is very recent. The same users with the same numbers and SIP connections had their transfers succeeding as early as 5 days ago. Call id of successful transfer: 
call_2fe53e8e8c71443351f635c38ab
Call id of failed transfer (same user): 
call_9da92964107939119d5d2a8d932
o
r
@Omar Ashraf | Community Lead Hi Omar, I just had this issue as well. Has something been updated in the last 3 days?
3 days ago call transfers were working fine, today they aren't. Using custom provider with SIP
o
Let me check with the team about this and get back to you.
r
That would be much appreciated
We are using Telnyx as well. So it may be this issue.
call_928e025722fca75adbeccf1eefb
is a call id of a failed outbound call.
Problem solved, I needed to add custom SIP headers in RetellAI in the call transfer function. X-Telnyx-Username Username
a
Thanks @RaspberryTech
@RaspberryTech just to clarify, the value of the header is the same SIP connection username you're using when importing the number to Retell?
r
Yes, so if your username in Telynx for the sip connection is 
admin
for example, you would set that as the value of the header
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