How to disable the Backpack based on Team?

Info; When the player is in the lobby they are transferred to the "Lobby" Team, when they are in the map they are transferred to the "Playing" Team. I would like for my script to disable the players backpack when they are in the Lobby, otherwise they can pull out their weapons and kill other players, which could stop them from loading into the map.

My current script is a local-script that is placed into StarterGui.

script:

game.Players.PlayerAdded:Connect(function(player)
	local theTeam = player.Team.Name
	if theTeam == "Playing" then
		game:GetService("StarterGui"):SetCoreGuiEnabled("Backpack", true)
	elseif theTeam == "Lobby" then
		game:GetService("StarterGui"):SetCoreGuiEnabled("Backpack", false)
	end
end)

I didn't really know what I was doing lol.

@DindinYT37's answer is almost correct, but he forgot that it should be used in the Client. (LocalScripts, ModuleScript required by a LocalScript, etc.)

To communicate with the Client on the Server, we can use a RemoteEvent. First, create a RemoteEvent inside ReplicatedStorage. Lastly, name it EnableBackpack.

Also @DindinYT37 you don't need to check when a Player joins the game, you can use Team.PlayerAdded when a Player joins the Team.

Server side (Script inside ServerScriptService or Workspace):

local Teams = game:GetService("Teams")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local Playing = Teams.Playing
local Lobby = Teams.Lobby

local EnableBackpack = ReplicatedStorage.EnableBackpack -- the RemoteEvent we'll use

Playing.PlayerAdded:Connect(function(newTeammate) -- when a player joins the team
	pcall(function()
		EnableBackpack:FireClient(newTeammate, true) -- if the player leaves/disconnects, it might error so we will do it in a pcall() to avoid errors
	end)
end)

Lobby.PlayerAdded:Connect(function(newTeammate) -- when a player joins the team
	pcall(function()
		EnableBackpack:FireClient(newTeammate, false) -- if the player leaves/disconnects, it might error so we will do it in a pcall() to avoid errors
	end)
end)

Client side (LocalScript inside StarterPlayerScripts or StarterGui):

local StarterGui = game:GetService("StarterGui")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local EnableBackpack = ReplicatedStorage:WaitForChild("EnableBackpack") -- the RemoteEvent we'll use

EnableBackpack.OnClientEvent:Connect(function(backpackEnabled)
	local success
	repeat
		success = pcall(function()
			StarterGui:SetCoreGuiEnabled(Enum.CoreGuiType.Backpack, backpackEnabled) -- disables the backpack
		end)
		task.wait()
	end
end)