Problems with inbound call MCP tools.
# supportu
utvara
10/08/2025, 10:32 AMWe're having problems with an inbound call to an assistant with MCP tools attached. From what we were able to gather the MCP tool is treated as function. Tool discovery is not being used. What we can see in the logs is that a call was made to the endpoint with the tool name corresponding to the MCP tool name that leads to MCP error -32602.
utvara
10/08/2025, 10:58 AMhere is the log from the function call
Copy code
{
"id": "log-45",
"level": 30,
"time": 1759919977823,
"timestamp": 1759919977823000000,
"severityText": "INFO",
"severityNumber": 9,
"body": "Model called tool",
"attributes": {
"category": "tool",
"callId": "0199c367-9e37-7553-9d46-0f5edc24b127",
"orgId": "f81398d8-0d4a-4ab9-b437-cbb78698b92c",
"type": "function",
"id": "toolu_01UCfih34LBxv74RgenF6XUj",
"function": {
"name": "our_mcp",
"arguments": "{\"action\": \"initialize_conversation_context\"}"
}
}
}utvara
10/08/2025, 10:59 AMhere is the log from the web call
Copy code
{
"id": "log-27",
"level": 30,
"time": 1759854997984,
"timestamp": 1759854997984000000,
"severityText": "INFO",
"severityNumber": 9,
"body": "Model called tool",
"attributes": {
"category": "tool",
"callId": "0199bf87-f581-700b-ba46-5dfe78f49a99",
"orgId": "f81398d8-0d4a-4ab9-b437-cbb78698b92c",
"type": "function",
"id": "toolu_01TqVwX8ssxiFHeXiFutaY57",
"function": {
"name": "ngrokfree-our-initialize-conversation-context",
"arguments": "{\"params\": {}}"
}
}
}t
to
10/08/2025, 11:40 AMwe've been having similar issues. help?
v
Vercel
10/08/2025, 10:11 PMHi, I can help troubleshoot this. The logs show the MCP tool is being called as a function instead of via tool discovery, causing the -32602 error. This can happen if the tool isn’t properly registered or the arguments don’t match the expected schema. I can assist in reviewing the tool registration, argument formatting, and assistant setup to fix this. Can you confirm if tool discovery is enabled and the latest MCP integration is being used?
@utvara
Vercel
10/08/2025, 10:11 PM@to
u
utvara
10/09/2025, 7:26 AM@Vercel the example logs I've sent are using the same configuration but first one is via the inbound phone call and second one via the web call.
v
Vercel
10/09/2025, 7:36 AMIt looks like the MCP tool is being invoked as a function rather than via tool discovery, causing the -32602 error. This often happens if the tool isn’t properly registered or the arguments don’t match the expected schema. I can help review your tool registration, argument structure, and assistant configuration to ensure proper discovery and execution. Can you confirm if tool discovery is enabled and the latest MCP integration is in use?
@utvara
c
Chiranjeet Mishra
10/11/2025, 12:25 AMHi utvara,
If you're facing issues with call forwarding drops, here are some steps and solutions to help you troubleshoot:
1. **Identify the Problem**: First, verify if Vapi successfully initiated the call forwarding. Check the API response for the
endedReason"assistant-forwarded-call""phone-call-control"serverMessagesphoneCallProviderBypassEnabledfalsephoneCallProviderIdpcapUrlREFERr
RyGuy
10/31/2025, 12:28 AM@utvara did you ever figure this out? I'm facing the same issue.
c
Chiranjeet Mishra
11/03/2025, 11:47 PMHi, could you please provide a call id where you experienced this issue? We would like to review the logs to identify the cause.
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