Small & Light 'Amazon Barcode '

Hi There I have an EAN printed on the item we are selling and have enrolled into small and light successfully after (mistakenly) selling through regular FBA. Those items are not inactive and removed after selling out.

I assumed the barcode on the item would work for small and light also but as I was working on the shipment it has said I cannot use the barcode and that instead it requires an Amazon Barcode - so I have to place a new one over the existing barcode.

Do I understand correctly? I have a perfectly functional EAN and corresponding barcode but instead I need to print new labels and place them over the manufacturers barcode?

Any experience or advice of this situation is much appreciated thanks