Beotalk 1200 and Beocom 5 known compatibility issues?

Just bought the latter, both plugged into the same phone line using the provided splitter - 1200 shows the telephone signal in the LCD.

Had to change to the Beoline transmitter too.

It does not answer now though records incoming calls as news. (Upgraded from a Beocom 6000 mk1 where all worked perfectly.)

Am I missing something other than a 20 year gap?