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. <EOS>