The Purchase of seats is only permitted on flights that are operated by Qatar Airways with a Qatar Airways flight number.
Please refer to the below examples:
If you have purchased your ticket from British Airways for a flight operated by Qatar Airways, then you will not be able to select a Preferred Seat.
BA7006 20MAR LHRDOH 0800 1745 OPERATED BY QR006
If you have purchased your ticket from Qatar Airways for a flight operated by British Airways, then you will not be able to select a Preferred Seat. Please refer to the below example:
QR5943 20MAR DOHLHR 0640 1110 OPERATED BY BA122