My mermaid sims never receive royalties from books or anything else, and my normal sims can. What happens is for example if they publish a book, the royalties will never pop up and it is almost like the book never existed. This also happens with nature documentaries and songs.
@elyeett It is a reported bug. The SimGurus are asking for saves, so if you want to help fix it you could send yours. See the post marked as solution:
https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-IL-Mermaid-Sims-don-t-get-royalties/td-p/8168369
