A computer server for payment processing, comprising: a network interface; a processor; a memory containing computer-readable instructions for execution by said processor, said instructions comprising: a terminal connection module for receiving a connection request from a payment terminal by way of said network interface, and forming an encrypted network connection with said payment terminal; a pairing module for receiving a pairing request identifying said payment terminal from a merchant sales terminal, and associating said payment terminal with said merchant sales terminal in a data structure; a transaction request module for receiving a first message from said merchant sales terminal defining transaction parameters in a first data format, generating a second message containing said transaction parameters in a second data format compatible with said payment terminal, and sending said second message to said payment terminal over said encrypted network connection; a receipt delivery module for receiving a payment credential message from said payment terminal over said encrypted network connection in said second data format, generating a receipt message in said first data format, and sending said receipt message to said merchant sales terminal, wherein the first message comprises an asynchronous communication parameter comprising a uniform resource locator, URL, and wherein sending said receipt message to said merchant sales terminal comprises sending said receipt message to the URL. a network interface; a processor; a memory containing computer-readable instructions for execution by said processor, said instructions comprising: a terminal connection module for receiving a connection request from a payment terminal by way of said network interface, and forming an encrypted network connection with said payment terminal; a pairing module for receiving a pairing request identifying said payment terminal from a merchant sales terminal, and associating said payment terminal with said merchant sales terminal in a data structure; a transaction request module for receiving a first message from said merchant sales terminal defining transaction parameters in a first data format, generating a second message containing said transaction parameters in a second data format compatible with said payment terminal, and sending said second message to said payment terminal over said encrypted network connection; a receipt delivery module for receiving a payment credential message from said payment terminal over said encrypted network connection in said second data format, generating a receipt message in said first data format, and sending said receipt message to said merchant sales terminal, wherein the first message comprises an asynchronous communication parameter comprising a uniform resource locator, URL, and wherein sending said receipt message to said merchant sales terminal comprises sending said receipt message to the URL. a terminal connection module for receiving a connection request from a payment terminal by way of said network interface, and forming an encrypted network connection with said payment terminal; a pairing module for receiving a pairing request identifying said payment terminal from a merchant sales terminal, and associating said payment terminal with said merchant sales terminal in a data structure; a transaction request module for receiving a first message from said merchant sales terminal defining transaction parameters in a first data format, generating a second message containing said transaction parameters in a second data format compatible with said payment terminal, and sending said second message to said payment terminal over said encrypted network connection; a receipt delivery module for receiving a payment credential message from said payment terminal over said encrypted network connection in said second data format, generating a receipt message in said first data format, and sending said receipt message to said merchant sales terminal, wherein the first message comprises an asynchronous communication parameter comprising a uniform resource locator, URL, and wherein sending said receipt message to said merchant sales terminal comprises sending said receipt message to the URL.