In order to ensure that you have eCommerce data flowing into your Google Analytics account you need to place a few gtags on some pages throughout your storefront.
Google Tag
Firstly the Google tag that references your account must be placed on all pages, so it is recommended that you add it to the Layout.
<!-- Google tag (gtag.js) -->
<script async src="https://www.googletagmanager.com/gtag/js?id=G-ABCDE12345"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'G-ABCDE12345');
</script>
Make sure you replace both locations where you see the 'ABCDE12345' with your account's id.