I don't know if this applies but about 2 years ago, I had a paper ticket bought at aa.com refused by LX. Apparently LX did not have ticketing agreement with AA. My ticket was actually issued on AF codeshare of the LX flight and AA has ticketing agreement with AF. I had to buy a walk-up one-way ticket from AF for that LX flight (LUX to CDG). Fortunately, after some emails back and forth with AA CS and finally mailing ticket receipts and unused AF /LX flight coupon, my credit card was directly credited for that one-way ticket. I also got a goodwill voucher from AA.