MIF_E31211285/public/landing/js/finish_payment.js

var timeleft = 5;
var downloadTimer = setInterval(function(){
  if(timeleft <= 0){
    clearInterval(downloadTimer);
    window.location.href = WEB_URL
  } else {
    document.getElementById("countdown").innerHTML = timeleft;
  }
  timeleft -= 1;
}, 1000);