Attempt to field 'UserId' error?

So this is my script, also if you could help me improve my datastore usage and stuff, that would be great and show me some things to limit with, that would really help, but other than that, I get this error that says "Attempt to field 'UserId'", my username is "trycode" and I was just testing the banning thing on myself.

This is the script:

game.Players.PlayerAdded:connect(function(player)
	player:WaitForDataReady()
	local datastore = game:GetService("DataStoreService"):GetDataStore("LocalHost")
	local banned = datastore:GetAsync(player.UserId"-Banned") or nil
	
	if player.Name == "trycode" then
		datastore:SetAsync(player.UserId"-Banned","test")
	end	
	
	if banned~=nil then
		local GiveBanGui = script.Banned:Clone()
		GiveBanGui.Parent = player.PlayerGui
		GiveBanGui.LocalScript.Disabled = false
		player:Kick("You have been banned!")
	end
end)

This is inside the local script in the ban GUI

script.Parent.Changed:connect(function()
_G.GiveBanReason = function(player)
	return game:GetService("DataStoreService"):GetDataStore("Localhost"):GetAsync(player.UserId"-Banned")
end

script.Parent.Frame.TextLabel = "You have been banned\nReason: ".._G.GiveBanReason(game.Players.LocalPlayer)
end

So yeah, if you can help me, then thanks :)

P.S. I'm making a game called Mouse Trap, read more about it on this studio: https://www.roblox.com/My/Groups.aspx?gid=4085786