Bruh, you sound mad young with that question but I'll answer it for you without prejudice.
You'll notice that when people get arrested for prostitution, the charges usually don't say "Prostitution".... They say "Solicitation." Because what is really illegal is *soliciting* prostitution services... advertising yourself as a prostitute, standing on the street corner waving at cars, etc. Or patronizing such a solicitor.
Once two people get together to fuck, what gifts they exchange is their own business. It's like, if you have sex with your girlfriend and right after you're done you take her to go shopping, or you give her money to get her hair done... Are they gonna arrest you and say that you paid for the sex? Of course not! So if a chick just *happens* to have sex with a rapper.... and afterwards he just *happens* to give her 5k.... that ain't nobody's business so long as she didn't public advertise that she'll fuck anybody for 5k.