Activation/Installation

I need some help.
I signed onto my son’s account, on my console, and purchased a copy of the Diablo IV: Vessel of Hatred - Ultimate Edition: Diablo IV.
When my son signs onto his console to play the upgrade, it indicates that the upgrade has been purchased; however, when he attempts to actually play the upgrade, it does not function.
How do I get his console to recognize the upgrade?
Any constructive advise would be greatly appreciated.

Go onto his account on his Xbox. Highlight the D4 icon in your Xbox menus and press the button with 3 lines on it. Select manage game. Make sure the expansion has a check in the box. If not check it and hit install.