There are undoubtedly royalties being paid as some (unknown) percentage of sales. The advance is essentially a loan against earned royalties. Publishers spread

There are undoubtedly royalties being paid as some (unknown) percentage of sales. The advance is essentially a loan against earned royalties. Publishers spread advances over numerous projects. The real money comes when a book sells well and the author earns royalties, unless that author is already a star and commands a very high advance like a former president, a sports star, movie star, and so on.