I booked a CW ticket from SFO to LHR with Avios, but I’m AA Platinum. How do I get BA to recognize this, so I don’t have to pay for seat assignments?
You need to change the reservation freq flyer number from BA to AA. If BA mmb does not work try AY or RJ mmb.
The way to avoid this in the future is to book the award for "
another person" . That
other person is a 99.99% clone of you but that happens to have a different freq flyer number/program.