In iTach Flex you are using a TCP window size of 1200 bytes. It is impossible to send commands longer than 1200 bytes (long IR codes for heat pumps). It worked fine on GC-100. I have tried both the socket connection on port 4998 and JSON POST on port 80. Both have same limitations. When are you going to fix this (deal breaker) ?
Cannot send more than 1200 bytes in one iTach Flex command