As a PPL you may not seek any remuneration for flying except for advertising opportunities for shared cost flights in the context of a bona fide flying club.
Here if, for example, three of you go flying you must pay at least a third of the overall cost.
If you take someone you know flying and they offer to share the costs that's OK too as long you pay your full share and you don't make it a condition of the trip that the passenger(s) contribute.