Steam is not recommended nor supported by FiveM or ESX, and I’m not sure why you need to have the steam prefix. However, if you insist you need to replace the existing function and variables.
This assumes you are using ESX Legacy.
server/functions.lua
ESX.GetIdentifier = function(playerId)
for k,v in ipairs(GetPlayerIdentifiers(playerId)) do
if string.match(v, 'steam:') then
--local identifier = string.gsub(v, 'steam:', '') This removes 'steam:'
return identifier
end
end
end
server/classes/player.lua
self.license = identifier