The Samsung ER-4915 uses 44mm bond paper rolls and an ERC-18 ink ribbon cartridge. The same paper roll is used in both the receipt and journal side. Only one ink ribbon is required and it prints on both the receipt and journal. The ER-4915 printer is known as an impact or dot matrix printer. It could use thermal paper in a pinch if that is all you had and it had a good ribbon installed.
Don't operate the ER-4915 without paper and ribbon installed. If you don't want to issue a receipt with every sale turn it off but keep paper installed. Never attempt to re-ink the cartridge, buy only new factory inked ribbon cartridges.