Linked from: https://support.boldcommerce.com/hc/en-us/articles/115003654926-Google-Analytics-Tracking-Product-Recurring-Order-Information

analytics.js

<script>
(function(i, s, o, g, r, a, m) {
  i['GoogleAnalyticsObject'] = r;
  i[r] = i[r] || function() {
    (i[r].q = i[r].q || []).push(arguments)
  }, i[r].l = 1 * new Date();
  a = s.createElement(o),
    m = s.getElementsByTagName(o)[0];
  a.async = 1;
  a.src = g;
  m.parentNode.insertBefore(a, m)
})(window, document, 'script', '//www.google-analytics.com/analytics.js', 'ga');

ga('create', '[tracking_id]', 'auto', {
  'allowLinker': true
});
ga('require', 'linker');
ga('linker:autoLink', ['[myshopify_domain]', '[domain]'], false, true);
ga('require', 'ecommerce');

//create a GA ecommerce transaction
ga('ecommerce:addTransaction', {
  'id': '[order_name]',
  'affiliation': '[myshopify_domain]',
  'revenue': '[total]',
  'shipping': '[shipping]',
  'tax': '[tax]'
});

//add items to the ecommerce cart
for (var i = 0; i < products_json.length; i++) {

  var item = products_json[i];
  ga('ecommerce:addItem', {
    'id': '[order_name]',
    'name': item.title,
    'category': 'Recurring Orders Checkout',
    'price': item.price,
    'quantity': item.quantity,
    'sku': item.title
  });

}

ga('ecommerce:send');
ga('send', 'event', 'Checkout', 'Successful Checkout');
</script>