[How to] Use Essentialmode for own scipt

Hello !
So i try to use essentialmode in my scripts. So i begin by testing if i can do that with the one basic function in essential mode call user.getIdentifier() in a client.lua ! I also put @essentialmode/server/player/wrappers.lua" in server_sripts {}!
But when i try to use the function consol print :

Someone know how to solve this ? Because in Essentialmode Doc say nothing about how to use there function!

Thanks for reading!