Originally Posted by
gatzdon
Just flew copa this past weekend. I was only able to get to the online checkin and seat selection using the e-ticket number and last name. Copa had a different confirmation number than what united gave me.
True. You can find the CM PNR on your UA reservation. There will be a link that says something like "other Arline PNR's."
That said, the OP tried with the e-Ticket number too, which should have worked.
Another alternative: Try the mobile website. Some people have reported that it worked when the regular website did not. You don't need to be on a mobile device to use it:
http://m.copaair.com/copaair/copaair.htm