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We have updated the receipt stub (merchant copy) for them to capture tips and signatures to show the payment ID for the barcode rather than the order id. The reason being that there may be multiple payments on the order so if they can look it up by that it will be much easier for them to adjust tip for example if needed.
With that being said, when the merchant is on the customer and/or order screen and use the scan or search bar they should be able to scan/enter the payment id and pull back the order and see the payment that matches.