How to make a player invitation like in Island Royale?

I'm trying to make an FPS Shooter game, where you can invite you'r friend to play together. Does someone know a video or a website, where I can find the solution? When i tried it with local scripts, it doesn't appear on the invited player's screen, and when i tried it with normal script, there was a lot of error messages. Here's the Local Script inside the Invite button:

Nam: Textbox, where you write the player's name I put some values inside every player's backpack, in 2 groups: 1. Inviter: Invited (string);Party1,2,3(string, the names of party members) 2. Invited: Inviter (string, the inviter's name);Accept(bool, accepted the invitation or not);PartyOwner(string, if the player is in a party, this is the party owner's name)

script.Parent.MouseButton1Click:Connect(function()
	
	local player = game.Players.LocalPlayer
	local inv = script.Parent.Parent.Nam.Text
	local invited = game.Players:FindFirstChild(inv)
	
	if invited then
	if invited.Name == player.Name then
		
		script.Parent.Parent.Nam.Text = "Its You"
		
	else
	
		if invited.Backpack.Invited.PartyOwner.Value == "" then
		
			if player.Backpack.Inviter.Party1.Value == invited or player.Backpack.Inviter.Party2.Value == invited or player.Backpack.Inviter.Party3.Value == invited then
			
				script.Parent.Parent.Nam.Text = "Already In Your Party"
			
			else
			
				invited.Backpack.Invited.Inviter.Value = player.Name
				player.Backpack.Inviter.Invited.Value = invited.Name
				script.Parent.Parent.Nam.Visible = false
				script.Parent.Parent.Wait.Visible = true
				wait(32)
				script.Parent.Parent.Nam.Visible = true
				script.Parent.Parent.Wait.Visible = false
				if invited.Backpack.Invited.Accept.Value == true then
					
					if player.Backpack.Inviter.Party1.Value == "" then
						
						player.Backpack.Inviter.Party1.Value = invited.Name
						script.Parent.Parent.Nam.Text = "Accepted"
						player.Backpack.Inviter.Invited.Value = ""
						player.Backpack.Invited.Accept.Value = false
						player.Backpack.Invited.Inviter.Value = ""
						invited.Backpack.Invited.Inviter.Value = ""
						invited.Backpack.Invited.PartyOwner.Value = player.Name
						invited.Backpack.Invited.Accept.Value = false
						invited.Backpack.Inviter.Party1.Value = ""
						invited.Backpack.Inviter.Party2.Value = ""
						invited.Backpack.Inviter.Party3.Value = ""
						
					else
						
						if player.Backpack.Inviter.Party2.Value == "" then
						
							player.Backpack.Inviter.Party2.Value = invited.Name
							script.Parent.Parent.Nam.Text = "Accepted"
							player.Backpack.Inviter.Invited.Value = ""
							player.Backpack.Invited.Accept.Value = false
							player.Backpack.Invited.Inviter.Value = ""
							invited.Backpack.Invited.Inviter.Value = ""
							invited.Backpack.Invited.PartyOwner.Value = player.Name
							invited.Backpack.Invited.Accept.Value = false
							invited.Backpack.Inviter.Party1.Value = ""
							invited.Backpack.Inviter.Party2.Value = ""
							invited.Backpack.Inviter.Party3.Value = ""
						
						else
						
							if player.Backpack.Inviter.Party3.Value == "" then
						
								player.Backpack.Inviter.Party3.Value = invited.Name
								script.Parent.Parent.Nam.Text = "Accepted"
								player.Backpack.Inviter.Invited.Value = ""
								player.Backpack.Invited.Accept.Value = false
								player.Backpack.Invited.Inviter.Value = ""
								invited.Backpack.Invited.Inviter.Value = ""
								invited.Backpack.Invited.PartyOwner.Value = player.Name
								invited.Backpack.Invited.Accept.Value = false
								invited.Backpack.Inviter.Party1.Value = ""
								invited.Backpack.Inviter.Party2.Value = ""
								invited.Backpack.Inviter.Party3.Value = ""
						
							else
						
								script.Parent.Parent.Nam.Text = "Party Full"
						
							end
						
						end
						
					end
					
				else
					
					script.Parent.Parent.Nam.Text = "Decilined"
					player.Backpack.Inviter.Invited.Value = ""
					player.Backpack.Invited.Accept.Value = false
					player.Backpack.Invited.Inviter.Value = ""
					invited.Backpack.Invited.Inviter.Value = ""
					invited.Backpack.Invited.PartyOwner.Value = ""
					invited.Backpack.Invited.Accept.Value = false
					
				end
				
			
			end
		
		else
		
			if invited.Backpack.Invited.Inviter.Value == player.Name then
			
				script.Parent.Parent.Nam.Text = "Already Invited"
			
			else
			
				script.Parent.Parent.Nam.Text = "Already In A Party"
			
			end
		
		end
	end
		
	else
		
		script.Parent.Parent.Nam.Text = "Player Not Found"
		
	end
	
end)

I know it's big and complex, but i hope someone can help me