Use this script on the Thank You Page in Shopify to send the values to GTM

rothys-thank-you-page-gtm-variables.js

<!-- Start: Send variables to GTM -->
<script type="text/javascript">
  {% if checkout.order_id or checkout.id %}
      var productId = "",
          isInsolesOnlyOrder = "true";
      {% for line_item in checkout.line_items  %}
          {% if line_item.product.type != 'Insole' %}
            isInsolesOnlyOrder = "false";
          {% endif %}
          productId += "{{ line_item.product.id }}";
          productId += ",";
      {% endfor %}

      // Remove the last comma from ProductId.
      if ( productId.indexOf( "," ) > -1 ) {
          productId = productId.slice( 0, -1 );
      }

      window.dataLayer = window.dataLayer || [];
      window.dataLayer.push({
          'isInsolesOnlyOrder': isInsolesOnlyOrder
      });
      window.dataLayer.push({
          'productId': productId
      });
  {% endif %}
</script>
<!-- End: Send variables to GTM -->