For me it sounds like you are working in Italy 
(and here they call it “experience”)
I also miss the “crisis” argument as a reason why they don’t pay you in your story
(serious mode on):
I have a similar ‘client’ at the moment. He convinced me to work for him and royalties will come when a product goes into production. I decided for myself to give it a try knowing there would be a big chance it wouldn’t go anywhere.
In the meanwhile I luckily got also some other clients that do pay and the only thing I can say is that working for somebody without knowing ‘if’ one day they will be satisfied or working for somebody with more or less clear goal is a lot different.
The only reason why I personally would continue is the fact that you are working on something that you can put in your portfolio anyway.
Don’t get over enthusiastic and pre-calculating any royalties in advance 
that’s just frustrating…
Keep up the good spirit and learn from it for a future possible client/conversation.