for the Webhook i always receive this Status Code from Stripe

Webhook Error: Webhook payload must be provided as a string or a Buffer (https://nodejs.org/api/buffer.html) instance representing the raw request body.Payload was provided as a parsed JavaScript object instead.
Signature verification is impossible without access to the original signed material.
Learn more about webhook signing and explore webhook integration examples for various frameworks at https://github.com/stripe/stripe-node#webhook-signing

I looked into it over a day now and cant figure out where the mistake is in my Code.

Here is the Code:

const functions = require("firebase-functions");
const admin = require("firebase-admin");
const express = require("express");
const stripe = require("stripe")(functions.config().stripe.secret);

// Initialize Firebase Admin SDK
admin.initializeApp();

// Initialize Firestore
const db = admin.firestore();

// Create an Express app
const app = express();

// Middleware to capture raw body for Stripe webhook
app.use(express.raw({type: "application/json"}));

// Stripe webhook endpoint
app.post("/webhook", async (req, res) => {
  const signature = req.headers["stripe-signature"];
  const eps = functions.config().stripe.webhook_secret;
  let event;

  try {
    event = stripe.webhooks.constructEvent(req.body, signature, eps);
  } catch (err) {
    console.error("⚠️Webhook signature verification failed:", err.message);
    return res.status(400).send(`Webhook Error: ${err.message}`);
  }

  // Handle the event
  switch (event.type) {
    case "checkout.session.completed": {
      const session = event.data.object;
      const userUid = session.client_reference_id;

      console.log("Checkout session completed:", session);

      if (session.payment_status === "paid") {
        try {
          await db.doc(`restaurant/${userUid}/branch/payment`).set(
              {
                paid: true,
              },
              {merge: true},
          );

          console.log(
              `Firestore updated for ${userUid} with payment information`,
          );
          return res.json({received: true});
        } catch (error) {
          console.error("Error updating Firestore:", error);
          return res.status(500).send(`Update Error: ${error.message}`);
        }
      } else {
        console.log("Payment status is not "paid".");
        return res.status(400).send("Payment status is not paid.");
      }
    }
    default: {
      console.log(`Unhandled event type ${event.type}.`);
      return res.status(400).send(`Unhandled event type ${event.type}.`);
    }
  }
});

// Use express.json() for other routes if needed
app.use(express.json());

// Export the Express app as an HTTP function
exports.stripeWebhook = functions.https.onRequest(app);

I cant figure out what is wrong i hope for the final help here 🙂

The Status Code to return 200 instead of 400