No "Add Kit" Button for players

I have added kits and players can redeem them fine using /kit WelcomeKit.

However, they can't use /kit as the "Add Kit" button is not there.

What could be causing this? Permissions for the kit have been set up to allow everyone to have the kit etc.

Only the admin "adds" kits, You create the kits, The one every player gets (on my server) is the "Autokit" which is a basic starter survival kit, all other kits can be chosen by typing /kit and this will give a list of available (not hidden) kits, some of my kits are hidden (Admin and npc (bots) kits) , Some other kits are only available when a certain hour target is reached in the ranks system,
Autokits and custom kits are explained in the documentation, I dont use the gui part of the plugin but nevetheless players cannot "add" kits they can only redeem them.
ahh that makes more sense!

Wasn't 100% sure of the plugin as I haven't used it properly before but thank you very much for getting back to me!