Mobile device payments

A computer-implemented method comprising:

• receiving, at a server computing system, a first message from a first device associated with a first identifier of a first user, the first message requesting a payment transaction utilizing first account information associated with the first user and second account information associated with a second user, the first message identifying the second user;
• responsive to receiving the first message, identifying, by the server computing system, a second identifier of the second user;
• sending, by the server computing system, a second message to a second device associated with the second identifier, the second message requesting the second device to approve the payment transaction, the second message including an approval code, wherein the second device is a mobile device;
• receiving, by the server computing system and from the second device, a third message including the approval code;
• determining, by the server computing system, that the third message was received within a threshold amount of time;
• and
• based at least in part on the third message from the second device including the approval code:
• obtaining, by the server computing system, the first account information associated with the first identifier of the first user;
• obtaining, by the server computing system, the second account information associated with the second identifier of the second user;
• and
• processing, by the server computing system, the payment transaction between the first user and the second user utilizing the first account information and the second account information based at least in part on the third message being received within the threshold amount of time.