Abstract: Transaction processing is performed by an integration hub (100) communicating with :a number of broker systems B1, B2 . . . Bn; and a number of manufacturer client systems (200). The hub (100) has a client-side interface with an access control mechanism for interfacing with client systems (200), and a broker-side interface with a different access control mechanism for interfacing with the broker systems. When an upload is received from a client for an offer for sale or purchase of goods a broadcast is performed in which a notification with a unique reply URL is sent to each of a selected group of external systems. Each response identifies a log-on page (400), however the full URL is different for each due to the extension query string (such as, “link=10”and “link=57”). A detector function (420) monitors the incoming strings and, using a database (421) determines automatically the identity of the party responding.