If the two parties agreed on forming a marriage contract between them in such a way that the paid money is considered as dower like the permanent marriage, then the marriage is valid. If she understands that the relationship allows her to have sexual acts in return for a fee, then it is adultery. The same can be said if she understands the relationship as a form of friendship.
There is no doubt that they deserve a very high punishment in the Hereafter. Almighty Allah said: â€œAs for those who disbelieve, their patrons are false deities. They bring them out of light into darkness. Such are rightful owners of the Fire. They will abide therein.â€ (2:257)
The punishment in this life is not our duty.