This doesn't mean you can have more than one pet active at a time but to store any pets you don't want active at the moment.
The pet shop
mypet-storage-Citizens trait of MyPet-NPC
all pets obtained by other sources than taming them
The amount of pets a player can store is limited by the following permission:
X needs to be replaced by the amount of pets a player should be able to store.
X needs to be smaller or equal than the
MyPet.Max-Stored-Pet-Count in the config.
Because the server needs to check a lot of permissions in order to check if the player is allowed to store more than his currently stored pets, this config setting jumps in and limits these checks.