How do you ask your boyfriend to pay for your nails/hair if he does?

I’ve seen women say that their boyfriend pays for their nails, hair, etc. Now for those who relate, do you ask? Or how does he end up sending you money like that? I have a boyfriend and I’ve never asked anything of him to pay for me, but I’m just curious as to how women have their partners send them money or how that even leads up.

Thanks (: