Why did I get charged out of nowhere?

I have a random charge of $6.40 on my cash app card for absolutely no reason, I tried to re-download an app, it had me put my card in and verify with my fingerprint and took the money. I know I probably should’ve read something but I didn’t really expect to get my money taken (by the way I was just about to use the money on the game I was downloading, ruined my entire night). Can someone explain why I got that charge and how I can get my money back