Config.Multichar value is not set to true

Such case is the most common thing that people do (to be more exact, doesn't) is to properly set the Config.Multichar value to true while being on ESX.

If you won't set everything properly before joining up ESX will create new empty user in the users table that will prevent you from joining up until you remove it. Here's more information about it.

ESX Legacy (latest versions)

Headover to the es_extended/shared/config/main.lua and find

Config.Multichar = GetResourceState("esx_multicharacter") ~= "missing"

And set it to:

Config.Multichar = true

Simple as that.