Example of receiving a POST request to the merchant endpoint URL that receives the payment information

server-side
app.use(bodyParser.json());
// "{Merchant endpoint that receives server's payment info}" POST request receiver
app.post("/payments/complete", async (req, res) => {
  try {
    // Get imp_uid, merchant_uid from req.body
    const { imp_uid, merchant_uid } = req.body;
    console.log(imp_uid, merchant_uid);
  } catch (e) {
    res.status(400).send(e);
  }
});

Example of calling the Get payment API with the i'mport payment ID (imp_uid) to retrieve the payment info.

server-side
app.use(bodyParser.json());
app.post("/payments/complete", async (req, res) => {
  try {
    // Get imp_uid, merchant_uid from req.body
    const { imp_uid, merchant_uid } = req.body;
    console.log(imp_uid, merchant_uid);
    // Get access token
    const getToken = await axios({
      url: "https://api.iamport.kr/users/getToken",
      method: "post", // POST method
      headers: { "Content-Type": "application/json" },
      data: {
        imp_key: "imp_apikey", // REST API key
        imp_secret:
          "ekKoeW8RyKuT0zgaZsUtXXTLQ4AhPFW3ZGseDA6bkA5lamv9OqDMnxyeB9wqOsuO9W3Mx9YSJ4dTqJ3f", // REST API Secret
      },
    });
    const { access_token } = getToken.data.response; // access token
    // Get payment info from i'mport server using imp_uid
    const getPaymentData = await axios({
      // Pass imp_uid
      url: `https://api.iamport.kr/payments/${imp_uid}`,
      // GET method
      method: "get",
      // Add access toke to Authorization header
      headers: { Authorization: access_token },
    });
    const paymentData = getPaymentData.data.response; // Payment info
    console.log(paymentData);
  } catch (e) {
    res.status(400).send(e);
  }
});

Example of comparing the actual payment amount with the payment request amount, performing fraud check on the payment amount, and saving the data in the DB.

server-side
app.use(bodyParser.json());
app.post("/payments/complete", async (req, res) => {
  try {
    // Get imp_uid, merchant_uid from req.body
    const { imp_uid, merchant_uid } = req.body;
    console.log(imp_uid, merchant_uid);
    // Get access token
    /* ...Omitted... */
    // Get payment info from iamport server using imp_uid
    /* ...Omitted... */
    const paymentData = getPaymentData.data.response; // Payment info
    // Get the requested payment amount from the DB
    const order = await Orders.findById(paymentData.merchant_uid);
    const amountToBePaid = order.amount; // Requested payment amount
    // Verify payment
    const { amount, status } = paymentData;
    // If amount matches. Processed amount === Requested amount
    if (amount === amountToBePaid) {
      await Orders.findByIdAndUpdate(merchant_uid, { $set: paymentData }); // Save payment info to 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 issued successfully. Account info ${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: "General payment successful",
          });
          break;
      }
    } else {
      // Amount mismatch. Forged/falsified payment.
      throw {
        status: "forgery",
        message: "Forged/falsified payment attempted",
      };
    }
  } catch (e) {
    res.status(400).send(e);
  }
});