Pablo_Ruiz_Muzquiz
I believe it’s critical that the URL syntax is corrected, I lost a few hours because of the inconsistency between this tutorial and the docs here Filtering, Locale, and Publication State for REST API - Strapi Developer Docs
long story short, the valid query has the form of
GET /api/books?filters[authors][hobbies][$contain]=“dance”
and not
GET /api/books?filters\[authors\][hobbies][$contain]=“dance”
beware of those pesky \