I get the answer from the Girl that I don`t reach enough money why should this not be a bug when I reach 600 (without Poster) and are above 500? (played without your fix)There is no bug there. Both triggered fine during my test. The poster guy is basically a useless quest, he does not contribute to the money you make to give the girl.
Depending on who you choose i.e. girl for independence or the girl for none, the money you get is from random people on the street, mostly the dudes(the same multiple dude walking fast).
They give you 75 dollars each for a grand total of 600 max based on if they want independence or not.