I need help from the community in figuring out something. I built a voice agent using Retell with custom MCPs. I am routing my number from twilio through SIP trunking since Retell doesn't give UK numbers. The problem im facing is in my workflow I need to send a message to the callers whatsapp but what happens sometimes is that the contact number of the caller is different from the number they are actually calling from.

Hey I can definitely help you out with this. So the issue is basically that when calls come through your SIP trunk setup, the caller ID you're receiving might not always be the actual number the person is calling from - this can happen due to how the call routing is configured between Twilio and Retell, or if the caller has some kind of forwarding/masking on their end. Quick question - are you extracting the phone number from Twilio's webhook data when the call comes in? Specifically, are you looking at the From parameter? And is this mismatch happening consistently with certain callers or randomly across the board?

I am extracting the nnumbers from Retell nnot twilio, and for most of the user it returns the current number but some of the numbers are incorrect

Got it, that explains it 👍 When using SIP trunking, Retell can sometimes return a proxy or normalized number for certain callers. Twilio is the real source of truth, so the fix is to map/override the caller number using Twilio’s From data instead of relying only on Retell. I’ve done this setup before and can help you fix it so WhatsApp always goes to the correct number. Happy to help if you want me to take this on. @Naufil Kamran

Yes can you guide me step by step on what i need to do

Hello @Naufil Kamran , your issue that the user have a totally different number than the one he is calling from and you want to send message to this number ? or its a formatting issue?

The issue is sometimes number shown on retell is completely different, not just a formatting issue.

Can you share a call id , and a screenshot of what you mean.

@Omar Ashraf | Community Lead For example the phone number on the second call, this isn't a valid number Call_ID: call_d8b7ed67b93a7015dd4643ea7cd https://cdn.discordapp.com/attachments/1455088067252850876/1455636699408371772/Screenshot_2025-12-30_at_11.59.23_PM.png?ex=695572d1&is=69542151&hm=27d36d6f3187dfa772cc700930ded5fe3f86ddfcd8990d0589aff3e781c12b30&

How its not a valid number and he is calling you and the call is working fine ?

Yes the call is working completely fine, the actual number of the user is 923051999666

Okay, the phone number the user is calling from is different from the one you want to send to, right ? Then why not ask the user for the phone number that you want to send message to , then you can extract this phone number using the extract dynamic variable function, or with a custom function parameters and send the message to him.

yes i have already implemented that as a solution, but as a user experience it is ot a good option

how else you want to get the phone number from the user , if you already have from some where else , you can send it as variable , or you can send the user message to write the number and send it back