The invention relates to a payment transaction method and system, whereby payment transactions are carried out between customers, with portable mobile appliances (1), for example, mobile radio telephones, and several payment terminals (2) in an office. The payment terminal (2), responsible for a payment transaction, informs the customer concerned of the transaction total amount and the transaction identification of the payment transaction. Said transaction identification comprises a payment terminal identification and an office identification. The payment terminal (2) transmits the transaction identification and the transaction total amount to a transaction centre (4) and the mobile appliance (1) transmits the transaction identification, which the customer inputs into the mobile appliance (1), to said transaction centre (4), by means of a mobile radio network (6). The transaction centre (4) transmits a payment request to the mobile appliance (1) which sent the transaction identification. A transaction document is prepared in the mobile appliance (1), which comprises a link between the payment request and a customer identification for the customer, and said document is transmitted from the mobile appliance (1), to the transaction centre, by means of a mobile radio network, whereupon the transaction centre transmits a transaction authorisation to the payment terminal (2) concerned.