Good luck with the Velo forum.
Meanwhile, I suggest you give my code a try. I’ve tested both examples, and they work.
The first example toggles each item independently. Once an item is expanded, it is left expanded until it is explicitly collapsed. As a result, multiple items can be in expanded mode at any one time.
The second example allows only one item to be expanded at a time. Whenever you expand one item, any other expanded item is collapsed.
Both examples toggle the button between ‘+’ and ‘-’.