This is an odd one, hands free starting works fine with red key held where the sensor is, but not with the fob key ... assuming the transponder has stopped working in the fob? And assuming it's a dealer job to sort out?
Done that Andy, no difference, it should work as a non-active key if the battery had run down anyway. But doesn't ...
Hey ho, and now it's working again ... Took battery out and left it 20 mins, tried active key as a passive (no battery) and it worked this time. Put battery back in and it's working as an active again. Go figure ...
There was a recall on the 2015 model key, maybe also worth checking with your dealer in case you're covered.
My 2015 key would need a new battery once a month. Ducati denied under warranty. When I got recall of key done it's fine now. I just have a lot of extra batteries.
My fob was consuming a battery a week. Dealer insisted I kept changing it for extra long life batteries and only after 2 months and going mad with them, they claimed a new one in warranty. Of course their first response was: "oh, we never saw this happening before." just like all the other common problems I had in this piece of shit. Ducati dealers. They are a joke!