I spent 3 hours fighting with ba.com and BA app trying to overcome this error.

I had booked a flight with American Airlines that is operated by BA from LHR to the USA.

In our case, the problem is AA transferred our passport and LPR/Greencard info in the correct format, but BA expects it in a different format: BA doesn’t appear to understand that the LPR card number is the one on the back of the card, not the USCIS Alien number (on the front of the card). So BA ask for the green card number, but really expect the USCIS number.

I finally defeated BA.com by using Chrome in incognito mode. I didn’t log in. I used “Manage My Booking”, using the BA booking code, rather than the one provided by AA.

BA, BA.com and BA App have really gone down hill. Terrible experience!