GA Enhanced Ecommerce via Tag Manager [Implementation Guide]

As you might know, Enhanced eCommerce requires a special kind of implementation. It goes way beyond your basic transaction tracking, and it would take a lot longer to implement, but the depth of the data would be definitely worth it.
Start off right
First and foremost, you have to enable Enhanced Ecommerce reporting for your Google Analytics view.
If you already have set up Analytics tracking on your site and you want to move to Tag Manager, we suggest creating a new GA property for testing purposes.
Having both tracking codes on the site might lead to counting the data twice for the same property.
To avoid this, you want to remo gve the standard GA tracking precisely at the moment when you add the GTM one.
Also, you want to thoroughly test the Tag Manager implementation before you put it live.
There is a debugging section towards the end of the article, which I am sure that will be useful.
For now, let’s go ahead with the core Tag Manager set up.
After you create an account and a container at tagmanager.google.com, it’s time to add the GTM code to the site.
There are three main elements which need to be added to the site in the following order:
the dataLayer variable declaration
Source: https://managewp.org/articles/15341/ga-enhanced-ecommerce-via-tag-manager-implementation-guide

source https://williechiu40.wordpress.com/2017/06/17/ga-enhanced-ecommerce-via-tag-manager-implementation-guide/