game.ReplicatedStorage.KickRequest.OnServerEvent:Connect(function(Player, Reason)
game.Players:FindFirstChild(Player):Kick("You've been kicked by for "..Reason)
end)
A player argument is implicitly passed when you use :FireServer. Since you’re wanting to kick a player which is not the LocalPlayer, you’ll need to still pass the name, but also define the LocalPlayer so it goes from (Player, string) to (Player, string, string).
game.ReplicatedStorage.KickRequest.OnServerEvent:Connect(function(_, Player, Reason)
game.Players[Player]:Kick("You've been kicked by for "..Reason)
end)