Money for sex!

Is it wrong to ask for money in excahnge for sex? If so why? These guys dont mind asking for the 😻 so why cant we ask for 💰. My problem right now is that im single with 2 kids semi struggling to pay bills and this guy just straight out ask when am i gonna let him fuck. I told him it depends on if he pays me. He then became offended that i asked for money 😕. He said hes never done that i explained that if hes been in a relationship then he has paid for sex, true or false?.. I have never asked for 💰 before but i have been with a few guys and think to myself if i would have charged them i wouldnt have to struggle.