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!

Given your thorough troubleshooting and the recurring "Failed to connect to MCP server" error, this appears to be a known intermittent issue with Vapi's MCP integration (especially with Zapier MCP). The best next step is to contact [Vapi Support](support@vapi.ai) or post in the [Vapi Discord #support channel](https://discord.com/invite/pUFNcf2WmH) with your tool call logs and setup details, as backend instability or session management bugs may be involved. This will help the Vapi team investigate and provide updates or a workaround. Sources: - [Vapi MCP Tool Documentation](https://docs.vapi.ai/tools/mcp) - [Vapi Support Options](https://docs.vapi.ai/support) - [Vapi Discord Community](https://discord.com/invite/pUFNcf2WmH)

Use the correct /sse MCP endpoint, disable gzip, verify X-Session-ID headers are received, pin to a stable MCP version, use a proxy as a fallback and contact Zapier support if you're still experiencing issues..

Hey! To help track down this issue, could you share: - The call ID - What response you expected to get - What response you actually got instead This would really help us figure out what went wrong!