Ocuma not support RTS/CTS and DSR/DTR hardware protocol.
You NEED do connect each other some pins in cable itself:
4 and 6 (DSR/DTR)
7 and 8 (RTS/CTS)
4 and 5 (RTS/CTS)
6 and 20 (DSR/DTR)
And only after this, all your setting will work.
Untill I changed the cable no sending/receiving were.