Bookings get migrated from the main part of Amadeus to FLY at 3 days to departure so I suspect using external Amadeus windows such as Finnair in those final 3 days isn't going to work at that point. Maybe it would work at 4 days to departure. There are a number of threads about this, it clearly works for some people but not others, but I've not been able to ascertain what detail / details separate those two groups. From the other threads using different sorts of browsers and / not being logged into BAEC when updating the PNR seems to be the mroe successful.