A method comprising: scanning by a first user device of a first user a machine-readable optical label displayed on a second user device of a second user, wherein the machine-readable optical label contains a one-way token; an issuer application on the first user device initiating an update request message including the one-way token and sending the update request message to a first authorizing computer; receiving, by a server computer from the first authorizing computer, the update request message including an interaction request for an interaction between the first user and the second user, the interaction request comprising interaction details including the one-way token and an interaction value, the interaction transferring the interaction value from the first user to the second user; parsing, by the server computer, the update request message to determine the one-way token; determining, by the server computer, a second user account identifier for a second account of the second user from the one-way token; substituting, by the server computer, the second user account identifier for the one-way token in the interaction details so as to include the second user account identifier in the update request message; determining, by the server computer, a second authorizing computer associated with the second user account identifier; sending, by the server computer, to the second authorizing computer, the update request message; and receiving, by the server computer, an update response message from the second authorizing computer, wherein the second authorizing computer updates the second account of the second user based on the interaction details. scanning by a first user device of a first user a machine-readable optical label displayed on a second user device of a second user, wherein the machine-readable optical label contains a one-way token; an issuer application on the first user device initiating an update request message including the one-way token and sending the update request message to a first authorizing computer; receiving, by a server computer from the first authorizing computer, the update request message including an interaction request for an interaction between the first user and the second user, the interaction request comprising interaction details including the one-way token and an interaction value, the interaction transferring the interaction value from the first user to the second user; parsing, by the server computer, the update request message to determine the one-way token; determining, by the server computer, a second user account identifier for a second account of the second user from the one-way token; substituting, by the server computer, the second user account identifier for the one-way token in the interaction details so as to include the second user account identifier in the update request message; determining, by the server computer, a second authorizing computer associated with the second user account identifier; sending, by the server computer, to the second authorizing computer, the update request message; and receiving, by the server computer, an update response message from the second authorizing computer, wherein the second authorizing computer updates the second account of the second user based on the interaction details.