MCP Server connection fails with 422 "invalid JSON response from dbconnector"

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1

Hi,

I'm trying to connect a custom MCP server to a Retool Agent, but the connection always fails with:

Error: invalid JSON response from dbconnector
HttpError { statusCode: 422, payload: Object }
  statusCode: 422
  error: "Unprocessable Entity"
  message: "invalid JSON response from dbconnector"
  data: null

I've tried:

  • SSE endpoint (/sse)

  • StreamableHTTP endpoint (/mcp)

  • Bearer Token authentication (confirmed working — other clients connect successfully)

  • The server is publicly accessible over HTTPS

The same error occurs with the official Atlassian MCP server, so this doesn't appear to be a problem with my implementation.

A similar issue was reported here with no resolution: Make.com MCP Server

Is MCP server support still in beta? Is there a known fix or workaround?

Thanks

David

4

Now all working.

D.

5

Hi @Davidkm David, glad to hear you got it working! What exactly did you do to get it sorted, if you don't mind sharing? Would be useful context for anyone else running into the same thing!