MCP Tool – Failed to connect to MCP server despite correct setup
Hi Vapi Support,
I'm currently unable to get my Zapier MCP tool to work, despite following the official setup exactly. The tool call is triggered correctly, but it consistently fails with the following error:
{
"name": "MCP_test",
"role": "tool_call_result",
"time": 1749165901060,
"result": "{"error": "Failed to connect to MCP server"}"
}
Current Setup:
GPT-4o model (not Mini or 4.1)
MCP tool created and connected in the Vapi dashboard
Correct MCP server URL from Zapier
Action is set to send an email (tested and published)
Tool is selected in assistant configuration
Prompt clearly states: "Use the MCP access automatically. Zapier knows what to do."
What I've already checked:
The tool call is being initiated (ToolCall ID is generated)
The Zap is published and works manually via test
I’ve tested with multiple Zaps and tools
I’ve waited between edits/tests (no rate limit issue)
A direct CURL request to the MCP URL succeeds
No response from the MCP server via Vapi
Known Issues:
Based on messages from the Discord community, others have reported similar MCP issues:
Session not found / 500 errors
MCPs temporarily not working with Vapi
MCP works only "some of the time" and then breaks
My suspicion:
This might be a bug related to session management or tool context sync between Vapi and Zapier MCP.
Can you please help me debug this issue or confirm if it's related to the ongoing backend changes?
Thanks in advance for your help!
I'm currently unable to get my Zapier MCP tool to work, despite following the official setup exactly. The tool call is triggered correctly, but it consistently fails with the following error:
{
"name": "MCP_test",
"role": "tool_call_result",
"time": 1749165901060,
"result": "{"error": "Failed to connect to MCP server"}"
}
Current Setup:GPT-4o model (not Mini or 4.1)
MCP tool created and connected in the Vapi dashboard
Correct MCP server URL from Zapier
Action is set to send an email (tested and published)
Tool is selected in assistant configuration
Prompt clearly states: "Use the MCP access automatically. Zapier knows what to do."
What I've already checked:The tool call is being initiated (ToolCall ID is generated)
The Zap is published and works manually via test
I’ve tested with multiple Zaps and tools
I’ve waited between edits/tests (no rate limit issue)
A direct CURL request to the MCP URL succeeds
No response from the MCP server via Vapi
Known Issues:Based on messages from the Discord community, others have reported similar MCP issues:
Session not found / 500 errors
MCPs temporarily not working with Vapi
MCP works only "some of the time" and then breaks
My suspicion:This might be a bug related to session management or tool context sync between Vapi and Zapier MCP.
Can you please help me debug this issue or confirm if it's related to the ongoing backend changes?
Thanks in advance for your help!
