Originally Posted by KARFA

It's up to BA though for check in to OTP-LHR, not AA. BA are your operating airline for the first leg of your booking. Your options are:

1. try online/BA app using the BA PNR which covers the OTP-LHR flight
2. try at T5 and ask BA to check you in and issue a bp
3. if 1 & 2 fail then get someone at BA to call OTP and check you in for your OTP-LHR flight - you can collect the actual bp at the gate in OTP