GraphQL Apollo Server Introspection error

I’ve been getting this error when I run npx diagnose-endpoint for my apollo client.

**Diagnosing https://localhost:3000/api/graphql
⚠️ Introspection query could not parse "POST body missing, invalid Content-Type, or JSON object has no keys." As valid json. Here is the error: SyntaxError: Unexpected token "P", "POST body "… is not valid JSON **

I’m setting up GraphQL as a next.js API endpoint. I’m pretty sure my schema and resolver have no errors.

This is my next.js api endpoint:

import { server } from "../../graphql/apollo";
import { NextApiRequest, NextApiResponse } from "next";
import Cors from "cors";

// Initializing the cors middleware
// You can read here: https://github.com/expressjs/cors#configuration-options
const cors = Cors({
  methods: ["POST"],
});

// Helper method to wait for a middleware to execute before continuing
// And to throw an error when an error happens in a middleware
function runMiddleware(
  req: NextApiRequest,
  res: NextApiResponse,
  fn: Function
) {
  return new Promise((resolve, reject) => {
    fn(req, res, (result: any) => {
      if (result instanceof Error) {
        return reject(result);
      }

      return resolve(result);
    });
  });
}

export const config = {
  api: {
    bodyParser: false,
  },
};

const startServer = server.start();

export default async function handler(
  req: NextApiReque`st,
  res: NextApiResponse
) {
  res.setHeader("Content-Type", "application/json");

  // Run cors middleware (to allow Apollo Studio access)
  await runMiddleware(req, res, cors);
  // run apollo server
  await startServer;
  await server.createHandler({ path: "/api/graphql" })(req, res);
}

I tried implementing

1. "micro-cors" and wrapped it around export default async function handler(
2. Adding middleware function
3. No CORS with just setting headers as res.setHeader("…")

None of them worked.