Abstract: A method of controlling updates to booking data corresponding to purchasable products includes, at an intermediate server connected with a booking server: obtaining and storing purchase initiation data including a transaction identifier and a client identifier; transmitting a request for product definitions to the booking server, according to the purchase initiation data; receiving and storing a product definition from the booking server in association with the purchase initiation data; generating an interactive message containing selectable product definition data, and transmitting the interactive message according to the client addressing identifier; receiving a product selection, responsive to selection of the product definition data in the interactive message at a client device; and generating a purchase instruction corresponding to the product definition and sending the purchase instruction to the booking server causing the booking server to update the booking data to reflect a purchase corresponding to