A point-of-sale system with a mobile payment feature includes an electronic display, one or more processors, and storage media storing a payment plugin to the point-of-sale system. The payment plugin sends ticket data representing a guest ticket over one or more data networks to an online service provider computer system; receives instruction from the service provider computer system to mark the guest ticket as designated for mobile payment; and causes user interface feedback on the electronic display that the guest ticket is to be paid via mobile payment. By doing so, the merchant is informed through their point-of-sale system that payment of the guest ticket will be facilitated by the online service provider. This alleviates the merchant from collecting payment from the guest before the guest leaves the merchant's premises and allows the guest to leave the premises as soon as the guest ticket is ready for mobile payment.