I’ve just visited Andorra.
There seems to be 3 main banks with ATMs there. All ATMs appear to be on the same network (the screens look identical apart from branding).
The bad news. All ATMs charge €7 to withdraw from a Monzo account (and Wise as well.. I tried both)
The weird part is, unlike most countries, the full withdrawal amount is taken from your account BEFORE you approve/decline the surcharge. When you do decline the surcharge, the amount is almost immediately refunded.
Having said that, almost everywhere takes contactless payments…. EXCEPT the local bus service.
I’d recommend FEDA Mou-te app. This will allow you to buy bus tickets online. It also has a bus network map/tracker, since Google Maps has no public transport info in Andorra.
If you really need cash, the local casino accepts debit cards with a 3% fee. I didn’t try it, so there may be a risk that they pay out in chips rather than cash.