Hello, I have been working on the transfers for two days, but I haven't been able to make them work. Part of the tests I’ve conducted were with two different assistants. One has a phone number configured with Telnyx and can make both inbound and outbound calls without issues. The other assistant has a free number from VAPI, and both assistants use different tools for call transfers. When testing outbound calls with Telnyx, the number is dialed differently, so the numberE164CheckEnabled option is disabled. I did this because I tested the transfers using both the E164 format and a prefix to rule out this as the issue. On the other hand, the assistant with the VAPI number also cannot make the transfer work. In both cases, I hear the message the assistant is supposed to say, but a few seconds later, the call ends. When reviewing the logs, I don’t find any errors. The last action I can see is that the transfer was completed, but the destination number never rings. Please, I have an application that we want to publish in a few weeks, and this is an essential function for the project. Timestamp | Call ID outbound using telnyx 2025-03-13 17:39:53 PDT | 87076f07-3e85-498b-a0ea-a4dc9f3d8894 Timestamp | Call ID inbound usign telnyx 2025-03-13 16:17:22 PDT | a44899b8-c29c-4be7-8951-6010fe8381f2 2025-03-13 15:53:51 PDT | f8c42603-894f-49ce-8545-f5598ba69a38 2025-03-13 15:43:21 PDT | 8c40bff0-1fe0-4886-9571-08fabf783069 2025-03-13 14:28:00 PDT | 2ac0ac11-8222-4468-ba56-fe2cc61d9b02 2025-03-12 14:31:19 PDT | 4ee3a729-39bd-4382-a394-0fce28adb8b6 Timestamp | Call ID outbound using Vapi Number: 2025-03-13 16:28:23 PDT | d002ab94-26a2-4a7b-855c-ef19196bfe6c 2025-03-13 16:24:41 PDT | 3b26172b-9983-4a9f-b0c7-093f3b22d48c https://cdn.discordapp.com/attachments/1349921096757153832/1349921096970797167/Screenshot_from_2025-03-13_18-19-18.png?ex=67d4db7d&is=67d389fd&hm=0a68a6444b972d31bbebc4bbea913fc6ed418b85f44b242383110d36583da222& https://cdn.discordapp.com/attachments/1349921096757153832/1349921097205682226/Screenshot_from_2025-03-13_18-27-36.png?ex=67d4db7d&is=67d389fd&hm=2aa3e52eb0f2d7902cc9e09f5cbafed84ed9f612db0a8131601218f985313f4e&

Hi there! I understand you're having issues with call transfers using both Telnyx-configured numbers and VAPI free numbers. Let me help troubleshoot this 🔍 Based on your description (call ends after the transfer message without the destination ringing), here are the most common causes and solutions: ### For Both Telnyx and VAPI Numbers: 1. SIP REFER Message Handling - VAPI uses SIP REFER by default for transferring calls - Ensure your receiving system (PBX) can properly handle SIP REFER messages - Many users report calls hanging up immediately after "Transferring the call now" without actually transferring [source](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1333917242195046464) 2. Configuration of transferCall Function - Verify your transferCall tool is properly configured in the assistant's tools array:

json
   {
     "model": {
       "tools": [
         {
           "type": "transferCall",
           "destinations": [
             {
               "type": "number",
               "number": "+1234567890"
             }
           ]
         }
       ]
     }
   }

[source](https://docs.vapi.ai/tools/default-tools) 3. Destination Number Availability - The destination number may be busy or unreachable, causing hang-ups on transfer attempts - Try testing with different destination numbers to rule this out [source](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1339614362742165606) ### For Telnyx-Specific Issues: 1. Number Formatting - Even though you've disabled numberE164CheckEnabled, ensure the destination number format is consistent - Try both with and without the E.164 format to identify if this is causing issues [source](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1333643719205361662) 2. SIP Gateway Issues - Users often experience "sip gateway failed to connect" errors with Telnyx

yeah, i test with and without E164 format and transfer tool configure as well

@15cm_de_dolor allow me some time to go through them and get back to you.

@Shubham Bajaj Thanks a lot

You are looking for this Plus make sure to contact telynx team to enable the SIP REFER feature for your account.

ok, on it, thanks! i will try that and comment

Sounds good! Hope all goes well, we're here to help if it doesn't.

@Shubham Bajaj @Sahil Thanks for the help, so far Twilio was the only one that allowed me to transfer calls, thanks for the support

Awesome.

Is there a problem with transferring using tools at the moment? I am literally getting nothing but hangups and have followed your guide to a T

@thenotoriousllama i solve this using a phone number from twilio

@15cm_de_dolor yeah I'm using Twilio now too

@thenotoriousllama At what step are you stopped? On execute tool or the forward?

Also, @thenotoriousllama did you turn on the SIP refer?

@Sahil when the tool initiates the transfer it dies

@thenotoriousllama can shared screen shots the tool and call log example?

Looks like model execute the tool but without parameters https://cdn.discordapp.com/attachments/1349921096757153832/1352345456184787014/Screenshot_20250320-111713_Chrome.jpg?ex=67ddad5a&is=67dc5bda&hm=6ffcfc67a4c12bff343ef3f2fc74fb15b99bec023e5477453873044bd91dbc5e&

@15cm_de_dolor @thenotoriousllama Checking if this has been resolved for you guys. If not, do share the call ID, I'll take a look.

@Shubham Bajaj thanks a lot, for my part it is resolved

Marking this ticket as Solved ✅

Hey thenotoriusllama, I'm facing the exact same issue with SIP REFER on Telnyx. I'd appreciate your help getting set up on an enterprise/commercial agreement if it is the only solution, as i prefer not to use twilio for the incoming call costs. I'll DM you for more details. Thanks!

This ticket has been marked as solved, and as a result, you will no longer receive any further responses. Kindly create a new support ticket to escalate your inquiry.