CPDLC does not work correctly on this aircraft, at least with SayIntentions.ai. They offer an ACARS/CPDLC connection that works with most, if not all other aircraft. I have tried it with a flight plan loaded into the FMS and without a loaded flight plan. Same end result. I have a copy of their support analysis if you want more information about this issue.
Gmail - Re_ Ticket #6334 _ CPDLC does not work in X-Plane 12. I requested a clearance and never got a reply. I used to get the _We are looking int….pdf
