Used Google flights to piece together a trip to Portugal next month.

It's all on one PNR (AA), but there is one IB codeshare and two BA codeshares.

I have the IB and BA PNR codes.

The BA website won't let me purchase seats in advance, and when I call the agent says he can't do it either, "because of how the flights were purchased".

I think the explanation has something to do with the fact that the BA flights are codeshares. But I still don't know how to convince BA to take my money (and a lot of it -- about USD 200 for 2 people on two flights).

So before calling BA again, I will ask here:

If I give BA all of the relevant PNR codes, should they be able to let me buy seats on BA flights? Surely the answer should be yes...

BTW, when I tried to do the same for the IB flight, I never got past the robotic part of their phone system ... ie dialing 2 for English never got me to English....