Assistant Transfer Randomly Failing
# supportc
Caleb
04/12/2025, 10:01 PMHey I have a sqaud of assistants and the entry assistant has this long array of assistants it can transfer to. I have noticed that if the User attempts to interrupt the AI's first message, that later when it attempts to transfer the call to the appropriate assistant, it always fails. Like it will say that 'transfering the call' line, and then just end the call.
This is a redacted example which occured earlier today:
AI
Good afternoon. Yeah. Thank you for calling [company name]. My name is [AI name]. Which location are you calling about today?
User
[location name]
AI
Good afternoon. Thank you for calling [company name]. My name is [ai name]. Which location are you calling about today?
User
[location name]
AI
Transferring the call now.
Forwarded ā
But it just forwards it to the grave š and hangs up.
Any clues on why this is occuring? And how to debug or resolve this?
v
Vapi Support Bot
04/12/2025, 10:02 PMHey there! š I see you're having issues with assistant transfers failing when users interrupt the AI's first message.
I wasn't able to determine the exact cause in your specific implementation without seeing your configuration or logs. However, I can definitely help with common causes and debugging steps for this issue!
Based on the information I found, here are some potential causes and solutions:
## Potential Causes
1. **Turn-Taking Behavior Issues**: When a user interrupts the AI's initial message, it can disrupt the expected flow, causing transfer failures. According to [information I found](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1335054553250533439), "This is how turn-taking behavior operates, the user must provide input in order for it to be processed by the assistant for the subsequent response."
2. **Timing Issues**: The transfer might be initiated before the AI has fully processed the user's interruption or completed its initial message. [One source](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1316539646808686602) indicates that transfers can fail when initiated immediately after a message that wasn't fully played.
3. **Misconfiguration**: There might be issues with your assistant's configuration, particularly related to
forwardingPhoneNumbertransferCallphone-call-controlVapi Support Bot
04/12/2025, 10:02 PM2. **Review Assistant Configuration**: Verify that the assistant ID is correctly set on the phone number and that there are no issues with the assistant request itself.
3. **Analyze Logs**: Check the Vapi dashboard and Twilio logs for any errors or unusual activity during the transfer process.
4. **Check Tool Call Details**: Examine the tool call details in the logs to see if the
transferCallnumWordsToInterruptAssistantmaxDurationSecondsassistantOverridesVapi Support Bot
04/12/2025, 10:02 PM- [Discord Thread about GPT4o success](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1339614362742165606)
k
Kings Big
04/12/2025, 10:07 PMTo help track down this issue, could you share one or two:
\- The call ID
\- When exactly this happened (the timestamp)
\- What response you expected to get
\- What response you actually got instead
This would really help us figure out what went wrong
c
Caleb
04/12/2025, 11:06 PM1. 2c016d8a-4bf3-4b6b-80c9-79310fafbdec . 2. Apr 12 2025 at 13:13 est (17:13 utc). 3. transfer to assistant called 'Red House Road - Main' . 4. "{
"name": "transferCall",
"role": "tool_call_result",
"time": 1744479116959,
"result": "",
"toolCallId": "call_NILYv9kgAZ18AYRgV7s2Pii1",
"secondsFromStart": 12.629
}" and then like it tried calling it again and this time "{
"role": "tool_calls",
"time": 1744479131041,
"message": "",
"toolCalls": [
{
"id": "call_qnxPwQ8EEWt9KVzLP27ASDIv",
"type": "function",
"function": {
"name": "transferCall",
"arguments": "{\"destination\": \"Red House Road - Main\"}"
}
}
],
"secondsFromStart": 26.711
}
{
"role": "bot",
"time": 1744479132474,
"source": "",
"endTime": 1744479133594,
"message": "Transferring the call now.",
"duration": 1120,
"secondsFromStart": 15.18
}
{
"name": "transferCall",
"role": "tool_call_result",
"time": 1744479132483,
"result": "",
"toolCallId": "call_qnxPwQ8EEWt9KVzLP27ASDIv",
"secondsFromStart": 28.153
}" where it just hung up the call .
a
Alex
04/13/2025, 5:32 AMI have exactly the same issue
k
Kings Big
04/13/2025, 5:54 AMCaleb we are looking into it
Kings Big
04/13/2025, 5:55 AMAlex, I recommend that you create a support ticket thanks
c
Caleb
04/13/2025, 2:42 PMGlad to hear im not alone lol. It's actaully a huge issue, causing a much worse UX for my customers
Caleb
04/13/2025, 9:12 PMAny update?
k
Kings Big
04/14/2025, 2:57 AMlogsKings Big
04/14/2025, 2:58 AMYour model triggered the tool call with a destination that was not in your transfer tool call destinations, so it pivoted to a number type and actually tried to forward the call. But because it was not a number, Twilio failed on their end (which he can verify in the Twilio call logs).
Now, you can also let him know that transfer to assistants only works within this squads, not out at the squads
c
Caleb
04/14/2025, 5:10 AMAhh okay thank you this was helpful
Caleb
04/14/2025, 5:11 AMIt looks like there was a SLIGHT variation in the assistant name in our prompt vs in the assistant destinations array
Caleb
04/14/2025, 5:22 AMI just pushed a code update. But can you confirm if that slight difference was causing the issue?
Caleb
04/14/2025, 5:28 PMHey so it solved lets say 80% of the problems HOWEVER there is still another underlining bug that i suspect is a system wide problem. here is a call_id for a call that occured just now "9738d745-485a-4b12-9e48-c51f12c1f8fa" . The User called and asked for a certain location - which triggers a tool call with to a new assistant called 'Tamiami Trail N. - Main-7fj' . It was properly set as 'name' for the assistant we want to transition to, in the assistantDestiation for the current assistant, and in the prompt. This transition occured flawlessly. However, once we are in that new assistant node, the user repeats a phrase once more which was the reason why the toolCall occured in the first place. This triggers ANOTHER toolcall to transfer to the assistant (but it is ALREADY ON that assistant , as we already did that transfer), and then therefore the call fails with these last 3 elements in that Messages array: "{
"role": "user",
"time": 1744651032515,
"endTime": 1744651033015,
"message": "Naples.",
"duration": 500,
"secondsFromStart": 14.16
}
{
"role": "tool_calls",
"time": 1744651033593,
"message": "",
"toolCalls": [
{
"id": "call_NUicYVjQ7N1vASvjwVKWm1Zt",
"type": "function",
"function": {
"name": "transferCall",
"arguments": "{\"destination\": \"Tamiami Trail N. - Main-7fj\"}"
}
}
],
"secondsFromStart": 14.368
}
{
"name": "transferCall",
"role": "tool_call_result",
"time": 1744651033608,
"result": "",
"toolCallId": "call_NUicYVjQ7N1vASvjwVKWm1Zt",
"secondsFromStart": 14.383
}".
Can you please do further investigate with this new call id to figure out the actually why that it has this odd circular logic for tool calling of assistants, even after we have successful done one? I suspect this is likely a VAPI-system issue occuring here, and a problem other Users are experiencing too
s
Sahil
04/15/2025, 5:22 AMcall_id pls
c
Caleb
04/15/2025, 4:36 PMliterally gave the call id if you wanna read it
Caleb
04/15/2025, 4:36 PM...
Caleb
04/16/2025, 6:27 PM@Sahil Bro please like this is MASSIVE issue that is occuring liteally on 10-25% of ALL CALLS
Caleb
04/16/2025, 6:28 PMIt is having MASSIVE negative implications for us. I just switched from Bland to VAPI, and I really would rather not have to mvoe to Pipecat
Caleb
04/16/2025, 6:29 PM@Kings_bigš«
k
Kings_bigš«
04/16/2025, 6:31 PMKindly resend your call id
c
Caleb
04/16/2025, 6:32 PM9738d745-485a-4b12-9e48-c51f12c1f8fa
Caleb
04/16/2025, 6:33 PMBro its literally in the 2nd sentence of the message...
Caleb
04/16/2025, 6:33 PMI gave you everything you needed to know to solve this in that message, and that just shows to me you didn't read it
Caleb
04/16/2025, 6:34 PMI get yall are busy af, but you Assistant tool calls are literally broken, and thats a big issue. This should be a critical issue ...
s
Sahil
04/17/2025, 2:51 PMUse gpt-4o
Sahil
04/17/2025, 2:52 PMand it is going to solve most of your issues.
Sahil
04/17/2025, 2:52 PM@Caleb
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