appCheckVerification middleware firebase functions v2

Question

I'm trying to implement a token verification as a middleware how firebase recomends.(https://firebase.google.com/docs/app-check/custom-resource-backend?hl=es-419)

The thing is When I try to test it using postman it doesn`t work.

Here is my middleware in my middleware file

import {request, response, NextFunction} from "express";
import {getAppCheck} from "firebase-admin/app-check";

export const appCheckVerification =
  async (req = request, res = response, next: NextFunction) => {
    const appCheckToken = req.header("X-Firebase-AppCheck");

    if (!appCheckToken) {
      res.status(401);
      return next("Unauthorized");
    }

    try {
      const appCheckClaims = await getAppCheck().verifyToken(appCheckToken);
      // If verifyToken() succeeds, continue with the next middleware
      // function in the stack.
      return next();
    } catch (err) {
      res.status(401);
      return next("Unauthorized");
    }
  };

This is my endpoint in my index file

import {onRequest} from "firebase-functions/v2/https";
import * as express from "express";
import * as admin from "firebase-admin";

admin.initializeApp();
const app = express();

app.get("/", [appCheckVerification], myEndpoint);

exports.myEndpoint = onRequest(app);

And in this image I'm giving to the endpoind the X-Firebase-AppCheck token as a header.

Any idea Why this is not working? The verifyToken never succeeds and I'm getting always 'Unauthorized' from the catch flow.

I'm trying to verify a token using firebase functions v2