Adding child to scrollbox not working

The issue could be a million things, you need to provide more information if anyone’s going to be able and willing to help resolve it.

Some questions:
Where is “this is my BP” happening? Inside a widget or another type of blueprint?
If you were to add “…item” widget to the viewport directly, without adding it to the parent, is it visible then?
What does the design tabs of the widgets look like.