Mods: RPG series mods (except Jewelry), BetterCombat, JEI, and Simply Skills installed.

When I open the survival inventory there isn't a slot above the shield or anywhere for a class specific book to go... I'm running the mods on Modrinth and tried running them in the normal launcher which didn't work... I've also tried removing Simply Skills which also didn't make the slot appear...

Wait... I fixed it. I didn't install Trinkets. I was looking through the Modrinth logs and found that one of the API's recommend trinkets which turned out to be a mod for slots and equipment...