Blueprint Communication, google it, watch tutorials, and understand nothing (like most of us after first time).
Hardest thing to get is knowing difference between some virtual Blueprint (BP code that is in content browser), and actual live blueprint somewhere with reference to it (pointer).
Your two UMG blueprints in browser are 2 virtual graphs, that are source code only, they are not placed in game. When you place them both in GUI blueprint as widgets they both are created in game.
And that is when they can communicate. This goes for all blueprints, to communicate they need to be “alive” in game.
So place them both inside umg hud blueprint (they need to be real blueprints not just abstract code in content browser).
Easiest to pass variable over would be either interface, or custom event dispatcher in text box blueprint, but that if you know interfaces or dispatchers.
If you do not know interfaces you need to pass variable manually.
- set text box widget as variable
- cast to it from master umg blueprint, read and store user name
- cast to display name bp, set user name variable there
- display name.
Or just use BP interface to pass value over. Sadly I am not at my pc now, and cannot write exactly how to do it without unreal editor in my face (not that good with interfaces yet, i prefer dispatchers).