Unable to send data from Stripe Webhook to Firebase Firestore - firebase

Question

I have made a Stripe webhook and I want to write data to Firebase when a Stripe purchase happens, and it isn't working although the payment always succeeds but the data is not sent to Firebase database.
In the following I will provide my code:
` import {
buffer
} from "micro";
import * as admin from "firebase-admin";
// <--SECURE A CONNECTION TO FIREBASE FROM THE BACKEND -->
const serviceAccount = require("../../../permissions.json");
const app = !admin.apps.length ?
admin.initializeApp({
credential: admin.credential.cert(serviceAccount),
}) :
admin.app();
// Establish connection to stripe. Stripe initialization
const stripe = require("stripe")(process.env.STRIPE_SECRET_KEY);
const endpointSecret = process.env.STRIPE_SIGNING_SECRET;
const fulfillOrder = async(session) => {
console.log("FULFILL ORDER", session);
return app
.firestore()
.collection("user")
.doc(session.metadata.email)
.collection("orders")
.doc(session.id)
.set({
amount: session.amount_total / 100,
amount_shipping: session.total_details.amount_shipping / 100,
images: JSON.parse(session.metadata.images),
timestamp: admin.firestore().FieldValue.serverTimestamp(),
})
.then(() => {
console.log(`SUCCESS: Order ${session.id} had been added to the DB `);
})
};
export default async(req, res) =>
// In next js if we want to check if we have a get request or post request, etc, we do in the following way
if (req.method === "POST") {
const requestBuffer = await buffer(req);
const payload = requestBuffer.toString();
const sig = req.headers["stripe-signature"];
let event;
// Verify that the EVENT POSTED came from Stripe
try {
event = stripe.webhooks.constructEvent(payload, sig, endpointSecret);
} catch (err) {
console.log("Error", err.message);
return res.status(400).send(`Webhook error: ${err.message}`);
}
if (event.type === "checkout.session.completed") {
const session = event.data.object;
return fulfillOrder(session)
.then(() => res.status(200))
.catch((err) => res.status(400).send(`Webhook Error: ${err.message}`));
}
}
};
// in order to implement webhook with NEXTJS we need to DISABLE few features in the config
export const config = {
api: {
bodyParser: false,
externalResolver: true,
},
}; `