<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>PromptPay QR Code Generator</title>
    <script type="text/javascript" src="js/jquery-3.2.1.min.js"></script>
    <script type="text/javascript" src="js/qrcode.min.js"></script>
  </head>
  <body>
    PP-id
    <input id="pp-id" type="number" placeholder="เบอร์โทรศัพท์, รหัสประจำตัวประชาชน, TAX ID" maxlength="13"/><br />
    <div id="qrcode" style="width:300px; height:300px;"></div>

    <script type="text/javascript">
      var qrcode = new QRCode(document.getElementById("qrcode"), {
      	width : 300,
      	height : 300
      });
      function makeCode () {
      	var elText = document.getElementById("pp-id");

      	if (!elText.value) {
      		elText.value="promptpay.github.io";
      	}

      	qrcode.makeCode(elText.value);
      }
      makeCode();
      $("#pp-id").
      	on("blur", function () {
      		makeCode();
      	}).
      	on("keydown", function (e) {
      		if (e.keyCode == 13) {
      			makeCode();
      		}
      	});
    </script>
  </body>
</html>

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>PromptPay QR Code Generator</title>
    <script type="text/javascript" src="js/jquery-3.2.1.min.js"></script>
    <script type="text/javascript" src="js/qrcode.min.js"></script>
  </head>
  <body>
    PP-id
    <input id="pp-id" type="number" placeholder="เบอร์มือถือ, รหัสประจำตัวประชาชน, TAX ID" maxlength="13"/><br />
    Amount
    <input id="amount" type="" placeholder="1000.00"><br />
    <div id="qrcode" style="width:300px; height:300px;"></div>

    <script type="text/javascript">
      var qrcode = new QRCode(document.getElementById("qrcode"), {
      	width : 300,
      	height : 300
      });
      function makeCode () {
      	var elText = document.getElementById("pp-id");

      	if (!elText.value) {
      		elText.value="promptpay.github.io";
      	}

      	qrcode.makeCode(elText.value);
      }
      makeCode();
      $("#pp-id").
      	on("blur", function () {
      		makeCode();
      	}).
      	on("keydown", function (e) {
      		if (e.keyCode == 13) {
      			makeCode();
      		}
      	});
    </script>
  </body>
</html>

Edit placeholder and add amount input :tea:
Edit placeholder and add amount input :tea:
