When i use "/accessories slot add valid necklace" it does not add the slot

The commands are currently undocumented and subject to change but that command adds the ability to add a given slot as valid for the given stack within the players hand to be equipped, if you want to adjust the slot amount you can either make a datapack or adjust the amount of a given slot from the config as found within the Accessories docs: https://docs.wispforest.io/accessories/home/