Originally Posted by
emma69
Nope, it was my UK details on the API.
Huh, so I guess airlines these days are super-cautious? It seems that your return ticket made them to check your entry eligibility into Canada, though technically they could just leave it to the people at UK airport that's going to check-in your return flight to Canada.
Another unlikely reason is that airline check-in counters somewhat double/help with CBSA (canadian border service agency) in monitoring border exit.
How do you check which passport is on the API btw?