In Javascript you can send via post, with the jquery post method:
<script src="//code.jquery.com/jquery-latest.js" type="text/javascript"></script>
Putting the following script:
$(function() {
    $('#sub').on('click',function() {
      var data = {pagando: '<?php echo "xxxxx"; ?>'};
       $.post('sua_pagina.php', data, function(rtn) {
             var e = jQuery.parseJSON(rtn);
              /* --- se prefirir, tem mais duas formas de fazer parse 
                var e = eval('('+rtn+')');
                 --- ou
                var e = JSON.parse(rtn);  */
               if (e.success) {
                  alert(e.message);
              }
        });
    });
});
On the body, put the button:
<input type="button" id="sub" value="PAGAR">
And in PHP, you do what you need and then return if you have a valid condition:
if (isset($_POST['pagando'])) {
    //faz o que você quer aqui dentro 
   echo json_encode(array('message'=>'sucesso!', 'success'=>'1'));
}
							
							
						 
um... $.ajax() ?
– SneepS NinjA
I get it, @Sneepsninja. He wants to do an ajax, but he doesn’t know it calls ajax :)
– Wallace Maxters