I just ran into a similar problem today. Working on setting up 1 way RS232 commands from a new XP-8. Commands are the same as I have used in another project, and I have confirmed with manufacture that nothing has changed. Check all cables and connectors, nothing.
So to test the XP-8 I made a small project with just a receiver we have in our boardroom that was running IR from an RP-6. Moved the ir eye to the XP-8 programmed a few buttons (ON / OFF etc). RM433 lights up, so do the correct ir ports and no control.
Tested IR codes in standalone and receiver works fine.
Checked T2-C remote, and xp-8, both have latest firmware.
Have to talk to RTI tomorrow.