Create dynamic button in widget

Hi guys,
I have a small problem, I am trying to add buttons to my widget, I understand that the child add node is used, but I can not find the way it works, so I come to your help to see if they tell me how you can fix it.
Variable Button refers to the widget that contains the button to add.

Widgetinterface is where I want to add the button

Array category contains the text shown in the button

I attach the error that appears after finishing the game mode

Error Blueprint Runtime Error: Accessed None trying to read property Button from function: ‘Create Category’ from node: Add Child in graph: Create Category in object: WidgetInterface with description: Accessed None

Attached image of the BP

First… Adding children Widgets is best to do with vertical/horizontal boxes.

Second, buttons cannot take in children added, which then I come back to the vertical/horizontal boxes.

Third, you might want to have the widget have an owner (eg, Player controller.0)