Hey Spookey0188,
I’m quite amateur with UE but, I would suggest you should check out the “UnrealMatch3” Project. It has many things for android development like in-app purchases, ads, touches, menus etc.
Also, my wild guess from my limited amount of “still-learning” knowledge would be to make a boolean condition, say “addFree”. Now, until “addFree” is false the showAdBanner function is ran.
Now, when the purchase happens the “addFree” boolean is set to True so that the showAdBanner is not run.
Possible problem I can think of is if a user un-installs and re-installs your game, the boolean might reset despite him making the purchase…But, you might know if there is a way to save the purchase and set the boolean to true for that player. Hopefully I was a help.