Google Tag Manager Code that must be placed on every page in the store should be placed in Layout / Edit Advanced Layout / Head Addendum.
In Tags, variables are used to capture dynamic values. To capture dynamic values (e.g.: passing the transaction value and products purchased to a conversion tracking tag) additional tag code must be entered into the Settings Section / Edit Policies Addenda and Disclaimers / Order / Affiliate Addendum. For Addendum Position choose, 'Body Paragraph'.