Override errant referrers

index.js

// on page with the payment/login button that they leave from
var link = document.getElementById('paymentOrLoginLinkElementID')
var href = link.getAttribute('href');

link.addEventListener('click', function(event){
  // before progressing to the link, save the referrer
  event.preventDefault();
  sessionStorage.setItem('ctxReferrer', document.referrer);
  window.location.href = href;
});

// on whatever page the payment provider redirects back to
// ..snippet..
analytics.load('writekey');
analytics.ready(function() {
  // see if there's a stored referrer
  var referrer = sessionStorage.getItem('ctxReferrer');
  if (referrer) {
    // if so, send "fixed" page call
    analytics.page({}, { page: { referrer: referrer }});
    sessionStorage.removeItem('ctxReferrer');
  } else {
    analytics.page();
  }
});