Trying to connect a Logitech K810 Bluetooth keyboard.

I can see the keyboard but when I try to connect nothing happens for a while, and I then get a pop-up saying keyboard disconnected.
In other distros I would get a pop-up asking for a passphrase to be keyed in on the keyboard, followed by Enter, and then have connection.
Could look like this is what is missing here.

Any ideas or alternatives to get my keyboard connected?