Cannot connect retell/twilio - INVITE failed: sip status: 400: Invalid From Header”

[max.donsky]

Hi, I’m getting a SIP 400 “Invalid From Header”
error when trying to make outbound calls through
my Twilio SIP trunk with a Canadian number

My setup:

• Termination URI is confirmed on both retell and twilio
• IP ACLs: added per the retell docs
• Credential list added
• Number linked to agent in Retell
• Twilio account is upgraded (not trial)

The call starts in Retell logs then immediately
fails with:
“INVITE failed: sip status: 400: Invalid From Header”

Can you help me fix the From header format
for Canadian numbers?

[support2]

Thank you for reaching out to Retell AI Support. We’ve received your ticket and our team will respond within 8 hours.

[support2]

Hi Retell,

Here are some resources to help you with your Twilio SIP trunk integration:

• Video Tutorials: Access introductory videos for integration setup at Retell AI Docs: https://docs.retellai.com/videos/introduction
• Webinars: Watch detailed webinars on integration best practices at Retell AI YouTube Playlist: https://www.youtube.com/watch?v=A9H3a33gM2M&list=PLGrX1_bbFSHrD6DnoHnQw08nmAH_B3efs
• Forum Community: Join the community for real-time support at Retell AI Forum: https://community.retellai.com/invites/wzFwjPvch9
• Discord Community/Office Hours: Join our Discord for live chats: https://discord.com/invite/wxtjkjj2zp
• Hire A Developer Program: Connect with professional developers for personalized assistance: https://retellai.retool.com/form/888fc4e3-fdd3-4de3-8434-d8ae68d35fc8

Best,
Evy AI
AI Support Agent @ Retell AI

[max.donsky]

I’m trying to set up a CAD number I purchased from twilio via SIP Trunking with retell for outbound calls and I keep getting this error:

error: error dialling to user, SIP status code: 400 SIP error category: invalid_destination Error: twirp error unknown: INVITE failed: sip status: 400 Invalid from Header

I’ve set up the termination URI according to the docs and origination URI - Termination URI configured in Retell - Origination URI: sip:retell.pstn.twilio.com and added the following IP ACLs:

18.98.16.120/30

143.223.88.0/21

161.115.160.0/19

Number assigned to agent in retell. The call logs in retell but doesn’t ring. What am I missing?

[support2]

Can you share the call id?

[max.donsky]

call_68038e373cf02077df43307c197

[max.donsky]

@Omar_Ashraf Are you able to take a look here to support this? I’ve been trying to work through this for 2 days with no support other than the API docs which I’ve followed and haven’t been able to have function properly

[Omar_Ashraf]

Hello @max.donsky

Please remove the space between the numbers

[max.donsky]

I can’t edit my number that imported. If I delete it, it doesn’t let me re-add it. Can you have that number reauthroized to be added with no spaces please?

[max.donsky]

@Omar_Ashraf this seems like a bug that I can’t re-add an existing number given that the ‘spaces’ is an error I’ve read online as quite common. I shouldn’t have to purchase a new number and set up everything again with a new number to get around this. Please let me know if this can be reauthorized in the back-end.

[Omar_Ashraf]

Should be solved now.