Maybe he's run out of funds, maybe he's got money squirrelled away in various places but they aren't the easiest to access, maybe he just wants to save that for emergencies.
In any case, he needs a source of income and he knows enough about the seedier sides of thing to know where to go. He can't get permanently hurt, doesn't have to worry about catching STDs, doesn't mind sex, doesn't think sex work is inherently shameful and there aren't many other jobs that will let him be drunk around the clock (or where he can just show up without credentials), so it's a perfectly logical and pragmatic decision in his mind.
Doesn't mean he wanted the team to find out.
Bonus: They find out because he gets into an incident* involving the police and Copley needs to scrub the police report.
*Surface googling says selling sexual services is not illegal in France (buying them is) but police are still jerks so maybe he could be arrested for public indecency or disturbing the peace? Or even just be on the report as the witness or victim of a sex work related hate crime.
Booker & team, Turning to sex work during his exile
In any case, he needs a source of income and he knows enough about the seedier sides of thing to know where to go. He can't get permanently hurt, doesn't have to worry about catching STDs, doesn't mind sex, doesn't think sex work is inherently shameful and there aren't many other jobs that will let him be drunk around the clock (or where he can just show up without credentials), so it's a perfectly logical and pragmatic decision in his mind.
Doesn't mean he wanted the team to find out.
Bonus: They find out because he gets into an incident* involving the police and Copley needs to scrub the police report.
*Surface googling says selling sexual services is not illegal in France (buying them is) but police are still jerks so maybe he could be arrested for public indecency or disturbing the peace? Or even just be on the report as the witness or victim of a sex work related hate crime.