Request ACS Resend
This message requests the ACS to re-transmit its last message. It is sent by the SC to the ACS when the checksum in a received message does not match the value calculated by the SC. The ACS should respond by re-transmitting its last message, This message should never include a “sequence number” field, even when error detection is enabled, (see “Checksums and Sequence Numbers” below) but would include a “checksum” field since checksums are in use.