It shows an Runtime Error " Property setter was expecting a com.google.appinventor.components.runtime.Button component but got a IntNum instead. Note: You will not see another error reported for 5 seconds."
Learn to use the Do It facility to inspect what is in your global variables, especially things that should be lists.
I see you calling a list of individual items "pairs", but each item in the list is not a pair (list of 2 items), but just a single Button component.
That's a sure road to confusion.
For a pairing game like this, there are invariant rules that must remain true during the game, and you don't implement them:
- A picture should appear in exactly two buttons.
- Once you have assigned a picture to a Button, the Button should no longer be available for assignment of another picture in the current round.
Search this board For Valentines Match for a sample.