Originally Posted by
Maze13
ETA was my guess too. Did you check mark the box in your itinerary asking for valid travel documents and did you also give BA your ETA number? It was mandatory for me for my last trip to the US (January 2018).
yup and ive never given them my ETA number, and i've been over 12 times on the current ETA on the same passport so never seen that as an issue before.