How do you give a tool if a player owns a gamepass?

For some reason, if I set the parent to the player, it clones the tool into the player, but if I set it to player.Backpack, then nothing happens.

GamePassId = 9058115

game.Players.PlayerAdded:Connect(function(player)
	if game:GetService("MarketplaceService"):UserOwnsGamePassAsync(player.UserId, GamePassId) then
		local BoomBoxClone = game:GetService("ServerStorage").Boombox:Clone()
		BoomBoxClone.Parent = player.Backpack
	end
end)