interjection
don't worry about it; never mind; it's OK
Casual encouragement after a small mistake or failure, similar to 'no worries' or 'shake it off'. Derived from English 'don't mind'.
from English don't mind
あ、ミスった。ドンマイ!
Ah, I messed up. No worries!
試合に負けちゃったけど、ドンマイ!
We lost the game, but never mind!