GE smart switch neutral power requirement
There was should have been a little Grey wire that came with your switch.

The NEUTRALS that are tucked away in the back of that receptacle need to have that grey wire attached - so undo the wire nut that has the whites all together and add the grey wire - place the wire nut back on.

Connect the Grey wire to the neutral connection on your new switch. 
That connection is probably located in the Lower Right corner across from the Line connection and has the writing Neutral on it - there is a brass screw on the side but also there are two holes on the back side to insert two wires.