I've found US's user interfaces (both online and at the kiosk) extraordinarily unforgiving when it comes to entering one's UA MP#.

On one recent occasion, I tried to put my MP in online, only to find that there seemed to be no way to enter a partner carrier loyalty number, either in advance or during online check-in.

As for the kiosks, there's an option to enter an alternate program #, but in my experience the instructions ("type xxxxxxxxxxx-UA," as I recall) are incorrect. I say this because I've keyed in the info using the prescribed format, only to have the system nevertheless attempt to charge me a checked bag fee. (I have UA status & am exempt from the fee, which is kinda the point of entering my MP#.)

Has anyone had better luck with this? Am I just missing something obvious?

And yes, I enter the appropriate program/# when I book flights, but the #$%!! online site my employer requires me to use typically fails to pass the info along correctly.