Google Merchant Customer Review Optin window not opening on order success page – Magento

I have integrated following code in my website order success page via GTM :

  <script src="https://apis.google.com/js/platform.js?onload=renderOptIn" async defer></script>
  <script>
  window.renderOptIn = function() {
   window.gapi.load('surveyoptin', function() {
    window.gapi.surveyoptin.render(
    {
      "merchant_id": 87654376,
      "order_id": "{{dl.order.id}}",
      "email": "{{dl.order.customerEmail}}",
      "delivery_country": "{{dl.order.deliveryCountry}}",
      "estimated_delivery_date": "{{dl.order.estDeliveryDate}}"
    });
});

}

I implemented a dataLayer in my page which is propagatting the needed variables in above code just fine. The above tag is firing just fine.

But the optin window for google merchant customer reviews is not opening. When above code was pasted in site html then the optin window was opening fine. But when implemented the above code through GTM, despite the tag being firing OK, the optin window is not opening. Please help.