You can pay for this with a credit card, but don't dare think of commissioning art of consenting adults having fun sexually, credit card companies (and PayPal) will de-bank you. Our systems are so screwed up. :/
GTA 6 has received a rating of PEGI 18, revealing mentions of "decapitation," the ability for players to snort cocaine at any time, "scenes of sexual fetishes," and much more.