<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>

<h1>Donate using bunq</h1>

<form method="POST">Enter donation amount:
    <input type="text" id="donateamount" />
    <input type="submit" value="Donate via bunq!" />
</form>

<script>
$('form').submit(function (e) {
    e.preventDefault();
    var inputValue = $('#donateamount').val();
    window.location = "https://bunq.me/ikgeefaanbw41/" + inputValue;
});
</script>


</body>
</html>