JK has always held power over KD since the start. He’s using money to convince KD to be his sex partner. He then uses every little thing he does for KD as a weapon (i.e. adding it to his debt, sexual acts, flat out disrespect) to keep him stuck. KD may have signed the contract, but he did not sign it under the guise of the acts portrayed thus far. When JK says “I’ll pay you for sex” he never mentions the abuse on the body, the level of degradation, or the inclusion of non consensual acts (not even including the scene with the actor from s1). The level of fame, wealth, and physical strength JK has over KD, along with the miscommunication on the ethics of their interactions, is what makes this non consensual.
It's not really lol. It's more on Kim Dan realizing the dynamic of their relationship is different from before. If let say Kim Dan knew he would be treated that way, then maybe he wouldn't have PTSD over it during dinner. Maybe there is a chance it could be consensual. Kim Dan at this point, his mental state is not at a place where he can given proper consent. This is shown when he said "I don't know anymore, I am just going with the flow" he was confused at Jaegang's treatment shift.

FINALLY SOMETHING CONSENSUAL ┗( T﹏T )┛