I'm not sure what to call it--as to whether it is a bug or an operator error, but I was attempting to fly MMCU to MMMZ, and the flight plan was successfully submitted. However, as following procedure, I logged on through Monterrey Center (MMTY), but I got the following message:

Thinking I had made a mistake, I attempted to log in as Mexico FIR (MMEX), Mazatlan FIR (MMZT), Mazatlan Oceanic (MMFO), Merida FIR (MMID), and then with KUSA (just out of a wild guess).

All of them, except for KUSA returned the same error code, while KUSA came back with "flight plan not held."

Is there a different FIR that I should be logging on to? And, if that's the case, is there a listing of FIRs that accept CPDLC authority?

MMFR is what I would have tried based on SkyVector.  However, when you file your flight plan on the HQ website, the response contains the CPDLC login authority, as well.

9 hours ago, Rob S. said:

MMFR is what I would have tried based on SkyVector.  However, when you file your flight plan on the HQ website, the response contains the CPDLC login authority, as well.

The one FIR identifier that I didn’t try! I was going off of the Mexico IFR charts.

Did Rob's solution solve the issue?