1. A method comprising: receiving, by a server system, from a mobile computing device a message listing identifiers of one or more in-store items and one or more online purchase items; processing, by the server system, a single payment of a total of the purchase prices associated with the identifiers; transmitting, by the server system, a verification code to the mobile computing device, the verification code indicating payment for the one or more in-store items; invoking, by the server system, fulfillment of an order for the online purchase items; receiving, by the server system, a verification message from an employee device, the verification message referencing the verification code; and in response to receiving the verification message, transmitting, by the server system, an electronic receipt to the mobile computing device.