While we most commonly associate Grooming with child grooming, Grooming is actually not restricted to child/adult scenarios. It can happen between two adults as well. It's only based on an individual manipulating/intimidating a victim who is an at risk/vulnerable person to coerce them to do what they want/exploit them.
In fact, Grooming doesn't even have to be sexual. Financial grooming is a very common form of grooming where the person slowly manipulates a victim in order to take control of the victim's finances.
The abuser typically befriends or builds a relationship with the victim in order to build a false trust which they plan to exploit later. Usually they will use gifts or promises to do this.
The main character is an at risk younger man who is in financial trouble and is basically on his own. The ML specifically treats him to dinners and sets up a relationship and later a contract where he can coerce him into sexual acts.

Instagram fooled me again :(