Help with invalid argument #1 to 'pairs' (table expected, got nil)

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#1

invalid argument #1 to ‘pairs’ (table expected, got nil)
I have no Idea what this means…
if you got any form of help this would be perfect

	
	if SetSuccess then
		Cash.Value = cash
		for i, cardID in pairs(cards) do
			for v, x in pairs(player.PlayerGui.Cards.Golds:GetChildren()) do
				if x.CardID.Value == cardID then
					local newcard = x:Clone()
					newcard.Parent = player.Cards
				end
			end
		end
		vien.Value = wins
		Gems.Value = gems
	end

is there something you'd like to see in this script? Let me know.
#2

You call pairs twice in this code and haven’t said which one is causing the error. However, the second one cannot produce that error because GetChildren() never returns nil. The “cards” you are passing to pairs in the first loop is nil. It must be a table.