Question about workers-mcp and "Unsupported content type: undefined" error

I've been experiencing issues using my deployed mcp servers from Claude Desktop. When I make an http request to the server, the server returns a json object with the expected format. When I try to call a tool in my Claude client, and can see from the logs using wrangler tail that a successful post request was made. However, no matter what I try, I keep seeing a "Unsupported content type: undefined" error. Does anyone have any experience building mcp servers using workers-mcp and know the proper way to format the response so Claude can interpret it?