To set the webhook's notification URL to send the payment information to, log in to the Admin console and then go to Payments->Live Settings tab and set the URL in the Endpoint URL field to receive the webhook data.

Content-Type can be specified as application/json or application/x-www-form-urlencoded. To test the URL, click the Test Webhook button to the right of the Notification URL field.

Set the notice_url parameter when calling the JavaScript SDK request_pay function to receive a webhook notification. Use this method to specify a different webhook URL for each payment request.

(If this parameter is specified, the Admin console's webhook setting is ignored.)

client-side
function requestPay() {
  // IMP.request_pay(param, callback) call payment window
  IMP.request_pay(
    {
      // ...Omitted
      notice_url: "https://Webhook URL", // Set Webhook URL
      // ...Omitted
    },
    function (rsp) {
      // callback
      if (rsp.success) {
        console.log(rsp);
      } else {
        console.log(rsp);
      }
    },
  );
}

curl -H "Content-Type: application/json" -X POST -d '{ "imp_uid": "imp_1234567890", "merchant_uid": "order_id_8237352", "status": "paid" }' { NotificationURL }

Create an endpoint to receive the webhook event's POST request as follows and then parse, verify, and save the payment information.

server-side
app.use(bodyParser.json());
// Route POST request to "/iamport-webhook"
app.post("/iamport-webhook", async (req, res) => {
  try {
    const { imp_uid, merchant_uid } = req.body; // Get imp_uid and merchant_uid from req.body
    // Get access token
    /* ...Omitted... */
    // Get payment info from i'mport server using imp_uid
    /* ...Omitted... */
    const paymentData = getPaymentData.data.response; // Save payment info
    // ...
    // Query for original requested amount from the database
    const order = await Orders.findById(paymentData.merchant_uid);
    const amountToBePaid = order.amount; // Original requested amount
    // ...
    // Verify payment amount
    const { amount, status } = paymentData;
    if (amount === amountToBePaid) {
      // Amounts match. Processed amount === Original requested amount
      await Orders.findByIdAndUpdate(merchant_uid, { $set: paymentData }); // Save payment info in DB
      switch (status) {
        case "ready": // Issue virtual account
          // Save virtual account info in DB
          const { vbank_num, vbank_date, vbank_name } = paymentData;
          await Users.findByIdAndUpdate("/* customer id */", {
            $set: { vbank_num, vbank_date, vbank_name },
          });
          // Send virtual account issuance text message
          SMS.send({
            text: `Virtual account has been issued. Account information ${vbank_num} ${vbank_date} ${vbank_name}`,
          });
          res.send({
            status: "vbankIssued",
            message: "Virtual account issued successfully",
          });
          break;
        case "paid": // Payment complete
          res.send({ status: "success", message: "Payment successful." });
          break;
      }
    } else {
      // Amount mismatch. Forged/falsified payment.
      throw {
        status: "forgery",
        message: "Forged/falsified payment attempted",
      };
    }
  } catch (e) {
    res.status(400).send(e);
  }
});