Hi there, flying from LHR to YYZ tomorrow at 4:20pm. For the past hour I have been trying to check in online but when I get past the number of bags I'm planning to check, it says online check-in is not available.

I see that I've been upgraded to WTP from WT so I'm assuming the flight is overbooked or they're changing equipment, or something which is the reason they won't let people check in online. Just wondering in these situations, does online check in usually become available eventually or will I have to do it at the airport?