Ducati Multistrada MTS 1200S D-Air Owner's Manual page 175

Hands Free (HF) Key not acknowledged
The activation of this "warning" indicates that the
Hands Free system does not detect the "active key"
near the vehicle.
Note
In this case, Ducati recommends making sure
that the active key is nearby (and that it was not lost)
or that it works properly.
174
Fig. 75