Looking for developer who has done Postilion xml configuration to POS system and is able to solve this aspect:
XML - TCP messages
Communication between the POS and the XML interface uses a TCP message beginning with a header to indicate the length of the data segment of the message. This header must precede all messages sent to the XML interface, and will be sent at the beginning of all TCP responses from the XML interface.
If the message length is less than 216-1 or 65535 then a two-byte header will be used.
The first byte of the header contains the quotient of the length of the message (excluding this header) and 256. The second byte contains the remainder of this division. Both these values are represented in binary as unsigned integer values ranging from 0 to 255 (bytes 0x00 to 0xFF).
If the message length is greater than or equal to 216-1 or 65535 bytes then a six-byte header will be used.
In this case the bytes 0xFF 0xFF should be sent followed by a four-byte length indicator, i.e. six bytes in total.