<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
<H1 id="H1"></H1>
<input type="button" value="Click Me" onclick="showMsg()">
<script>
    function showMsg()
    {
        var userInput;
        userInput = confirm("Press OK if payment is DONE, Else Cancel");
        if (userInput==true) {
            document.getElementById("H1").innerHTML="Payment is Done";
        }
        else {
            document.getElementById("H1").innerHTML="Payment is Not Done";
        }
    }
</script>

</body>
</html>