I want to give an item on join

Well well, there are different types of methods in this case, let's explain both:

Give an item on first join (so the item is only given ONE time)

Just enable the feature giveFirstJoin more information here https://docs.ssomar.com/executableitems/configurations/item-configuration/item-features#custom-give-first-join-settings

Give an item on each join

That is not correctly handled by EI, you can do it only if you have an item that is ALWAYS in the player inventories, something that most servers dont have, the best way to achieve this is using ExecutableEvents.