Suppose I went to a mall & got myself some t-shirts & tracks, I paid for them via the barcode attached individually on each clothing,
How can the store get to know that I have paid for them, if not then, How can I be caught by the store/system if I try to sneak out of the store?
If each item (not item type!) has its own different bar code, then it's straightforward: each such bar code corresponds to an entry in the database and it's also scanned by the cashier.
It will reflect the price and it will also mark the barcode paid when the payment is done.
But simple barcodes may not offer enough numbers for this task, I would use bigger range, plus ordered numbers may give ideas to hackers. I'd advise at least GUID as QR code for the job, if the scanners can handle that.
I'm not sure where you need cryptography for this though, since it's your own database.