Adding Google Tag Manager (requires an act of God?)

[mfs-mindsize]

We're trying to install GTM on a non-Plus store. 

We've added the snippet to: Online Store > Preferences > Additional Google Analytics JavaScript. 

Works fine on the store. 

However, on the Shopify checkout page, that code in that testarea is escaped. That is, for example " become &quote;

The client naturally wants analytics for the entire experience / process. 

How do we get GTM working? 

[Fred12268]

@mfs-mindsize  also you may install this https://drive.google.com/file/d/1Z1T-2USadcKXnpYNQGYC-00GBk0SUuyl/view?usp=drivesdk i will detect everything.