Only the variables defined in the Joi schema will be allowed. If the post body contains any extra fields, the entire request will be dismissed.
In this case, you’re sending a nested genre object in your post body, but in the Joi schema you’ve not defined genre . On the other hand, you’ve defined genreId which is not present in the post body.
You can do one of two things.
Remove genreId and define genre in your Joi schema as follows