How to fix "Argument 1 missing or nil" when turning strings into ints without result being nil?

So I'm tryna create an admin script. This error is occurring at Line 53. Using print() I have identified the issue which is that the tonumber() function is turning a string of numbers into nil. However, if I remove the tonumber() function from that line and leave it as a string I get the error "unable to cast string to int64".

This is meant to detect if a player is within a certain group, that group is being detected in the table "Settings.Banned".

----------------------------------------------------
--             		 Settings             		  --
----------------------------------------------------
local Settings = {}
	
Settings.ToolStorage = game:GetService("ServerStorage")
Settings.Moderators = {} 		-- Mods									Format: {"Username:UserId", "Group:GroupId", "Group:GroupId:RankId"}
Settings.Admins = {}    		-- Admins								Format: {"Username:UserId", "Group:GroupId", "Group:GroupId:RankId"}
Settings.Owners = {}	 		-- Owners								Format: {"Username:UserId"}
Settings.Creators = {}			-- Creators								Format:	{"Username:UserId"}
Settings.Muted = {}		 		-- Muted players						Format: {"Username:UserId"}
Settings.AdminBlacklist = {} 	-- Blacklisted from using admin			Format: {"Username:UserId", "Group:GroupId", "Group:GroupId:RankId"}
Settings.Banned = {"MeqoIo:497574391", "Group:497574391:255", "Group:2969826"} 			-- Banned players						Format: {"Username:UserId", "Group:GroupId", "Group:GroupId:RankId"}
Settings.Permissions = {} 		-- Command Permissions				 	Format:	{"Command:AdminLevel"}
Settings.MusicList = {} 		-- Music list 							Format: {"MusicId:Name"}

Settings.SaveAdmins = true		-- Saves admins using datastores
Settings.SaveBanned = true		-- Saves banned players using datastores

Settings.EnableTrello = false 	-- Is trello used to save data?			NOTE: The Main Admin Trello will over-ride this setting for exploit protection.
Settings.PrimaryTrello = ""		-- Primary Trello Board					Format: "BoardID"
Settings.TrelloAppkey = ""		-- Your trello appkey (DO NOT SHARE)	Link: https://trello.com/app-key
Settings.TrelloToken = ""		-- Your trello token (DO NOT SHARE)		Link: https://trello.com/1/authorize?expiration=never&name=Olo_Admin_Commands&key=APP-KEY

Settings.CreatorPowers = true	-- Used to give me (Meqolo) admin for debugging purposes
Settings.ChatCmds = true		-- Allows commands to be ran through the chat

Settings.ServerLockMessage = "Server currently locked"	-- Message sent when players kicked because the server is slocked
Settings.MaxLogs = "250"								-- Amount of logs stored before deleting them.

Settings.Console = true			-- Allowes a console to be used when "~" is pressed

----------------------------------------------------
--             	 End of Settings             	  --
----------------------------------------------------


local DSS = game:GetService("DataStoreService")
local Banlist = DSS:GetDataStore("Banlist")
local Modlist = DSS:GetDataStore("Modlist")
local Adminlist = DSS:GetDataStore("Adminlist")
local Ownerlist = DSS:GetDataStore("Ownerlist")


game.Players.PlayerAdded:Connect(function(plr)
	local pat = "(%a+):(%d+)"
	for i,v in pairs(Settings.Banned) do
		if string.sub(v,1,5) == "Group" then	
			local f = string.sub(v,7,string.len(v))
			print(f)
			f = tonumber(f)
			print(f)
			print(plr:IsInGroup(f))
			if string.sub(v,7,string.len(v)):gmatch("(%f+):(%d+)") then
				for ke,va in string.sub(v,7,string.len(v)):gmatch("(%d+):(%d+)") do
					print(ke)
					print(va)
					if plr:GetRankInGroup(tonumber(ke)) == tonumber(va) then
						plr:Kick("Banned")
					end
				end
			else
				print(string.sub(v,7,string.len(v)))
				if plr:IsInGroup(tonumber(string.sub(v,7,string.len(v)))) then
					plr:Kick("Banned")
				end
			end
		end 
		
		for key,val in v:gmatch(pat) do
			if plr.UserId == val then
				plr:Kick("Banned")
			end
		end
	end
	local Banned = Banlist:GetAsync(plr.UserId) or false
	if Banned == false then
	else
		plr:Kick("Banned")
	end
end)

The main block of code causing the error is:

			local f = string.sub(v,7,string.len(v))
			print(f)
			f = tonumber(f)
			print(f)
			print(plr:IsInGroup(f))

Just check if f isn't nil after you use tonumber (any non-number strings used in tonumber will return nil):

if string.len(v) > 7 then
	local f = string.sub(v,7,string.len(v))
	print(f)
	f = tonumber(f)
	if f then
		print(f)
		print(plr:IsInGroup(f))
	end
end

Fixed it myself, just needed to turn f into a string first.