If you have installed the Stape Server GTM Shopify app and it does not work, please check if: 

• You have followed all the steps in the article correctly https://stape.io/blog/server-side-tagging-for-shopify.
• The data layer is working in the web container preview.
  
  
• Also, please check that the plugin is active:

Online Store -> Themes -> Customize button on your active theme -> On the left side choose 'App embeds' item -> Make sure that GTM plugin is active.