This is a glitch with the UA OLCI system. When doing mobile check-in, if you're not a US citizen, the mobile app will tell you to go to the check-in counter. However, if you are a Canadian Citizen ,US PR or Citizen, OLCI on the normal website (i.e. desktop) works just fine. I've raised this issue with UA several months ago but it hasn't been addressed yet. I guess I'll be using good ol' fashioned OLCI on my trip to SIN next month (which isn't a big deal given the UA app doesn't support my Moto G6).

Safe Travels,

James