I’m implementing Stripe webhook integration on my Node/Express.ts backend running on Firebase Cloud Functions, and I’m struggling to pass the raw req.body during signature verification.

I’ve made a dozen attempts and fixes, and the error I keep encountering is: “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.“

Here is my index.ts:

const app = express();

app.use(cors());
app.use(allowedOriginsHandler);

app.post("/api/v1/stripe/webhook/payment", express.raw({ type: '*/*' }), listenToPaymentEvents);

app.use(express.json());

app.use("/api/v1", routes);

app.use(errorLogger);
app.use(errorResponder);
app.use(failSafeHandler);

export const httpFunction = functions.https.onRequest(app);
//admin.initializeApp();

//MARKETPLACE CLOUD FUNCTIONS
//orders
export const onOrderDocumentCreateFunction = onOrderDocumentCreate;
export const onOrderStatusChangeFunction = onOrderStatusChange;

//check order products availability
export const onOrderByVendorCreateFunction = onCreateOrderByVendor;

//products (create/update subcollections)
export const onProductDocumentCreateFunction = onCreateProduct;
export const onProductDocumentUpdateFunction = onUpdateProduct;

//Update seller public info collection on seller create/update
export const onSellerCreateFunction = onCreateSeller;
export const onSellerUpdateFunction = onUpdateSeller;

export const onUserRegistrationFunction = onUserRegistration;

// Create seller products bulk upload template on seller create
// and update seller document with the template url info
export const createSellerBulkUploadTemplateFunction =
  createSellerBulkUploadTemplate;

Here is the configuration for the other routes:

const router = Router();


router.route("/newsletter").post(addContactToNewsletter);

router.route("/checkout").post(
  firebaseAuthenticationHandler,
  checkProductsAvailabilityHandler,
  checkProductsPriceChangesHandler,
  lockProductsHandler,
  checkout
);

router.route("/order/vendor/cancel/:id").put(
  firebaseAuthenticationHandler,
  orderCancelledByVendor
);

router.route("/order/buyer/cancel").post(orderCancelledByBuyer);

router.route("/order/vendor/processing/:id").put(
  firebaseAuthenticationHandler,
  updateOrderToProcessing
);

export default router;

And this is the controller handling the webhook:

dotenv.config();
const stripePaymentIntentWebhookEndpointSecret =
  process.env.STRIPE_PAYMENT_INTENT_WEBHOOK_ENDPOINT_SECRET ?? "";

export const listenToPaymentEvents: RequestHandler = async (req, res) => {
  const sig = req.headers["stripe-signature"];

  if (!sig) {
    console.log("Missing Stripe signature");
    res.status(400).send("Missing Stripe signature");
    return;
  }

  let event;

  try {
    event = stripe.webhooks.constructEvent(
      req.body,
      sig,
      stripePaymentIntentWebhookEndpointSecret
    );

    switch (event.type) {
      case "payment_intent.payment_failed": {
        const paymentIntentPaymentFailed = event.data.object;
        console.log(paymentIntentPaymentFailed);
        break;
      }
      case "payment_intent.succeeded": {
        const paymentIntentSucceeded = event.data.object;
        await handlePaymentIntentSuccess(paymentIntentSucceeded);
        break;
      }
      default: {
        console.log(`Unhandled event type ${event.type}`);
      }
    }

    res.status(200).send("Event received");
  } catch (error) {
    if (error instanceof Error) {
      res.status(500).send(`Webhook Error: ${error.message}`);
    } else {
      res.status(500).send("Webhook Error: An unexpected error occurred");
    }
  }
};

What am I doing wrong?