Do I give him back 80 or 40 $ ?

Im a bit confused lol. My boyfriend and I said we were going go half and half on a hotel room for one night. The room is 80 and I was going to pay it with my card and he zelle me sending 80 and I would send him back half of it which is 40 but I accidentally used his card so he payed 80. Now I gotta send him back his money but do I send his 80 $ or 40 ?

Do I give him back 80 or 40 $ ?
Post Opinion