If you are viewing the data fine, and it is appearing without errors, then the ibus to COM port receive is OK

But if you cannot talk to anything, then the COM port to ibus is not working

When NavCoder sends a command, it appears on the ibus and appears on the NavCoder screen. So watch the bus data when you send a command - do you see it?

If you don't, check the interface!

Common problems:
Interface fault
Tx line not connected
Another device is using the COM port
problems with USB-to-Serial converter