Custom Template Drag and Drop not working with Universal Content

Hi!

I have got a hand coded Template. 

I have inserted the drag and drop code in the Template so i can drag in modules.

This works with Klaviyo blocks, but does not work with Universal content. 

The documentation says it should work with universal content, but it’s not allowing me to drag them in. When i drag the content over, the highlighted section does not even show, like its not even registering it.

Please could someone let me know if,

1. this is actually supposed to be possible? or
2. How can i get this working? 

Thank you,

Sarah