I guess there are no examples (yet?) because until now everybody was using in game currencies to deal with that.

But could you not give a player a voucher that says “-5€ on your next checkout” ? And then they get exactly that.

Yeah I know that people do that. What I wanted to say I that nobody clicks on MY profile pictures.

Or my jokes and easter eggs that I hide in those pictures are not funny enough for them to text me about it :/

I used to edit my WhatsApp profile pictures to have small Easter eggs in the corners that only those people see who click on the picture. Turns out nobody clicks on my profile picture.