Welcome 
A couple of things:
Wiring:
From your description I’ll assume you have a metal box with power coming in on a black and white wire.
If wired properly the Black wire is the Line and the White wire is the Neutral
Safety Ground is accomplished by connecting the dimer to the metal box (via the mounting screws). Please reply if this is not what you have.
Flicker:
There are several reasons, before we go off on a tangent can you tell us if the above white wire is connected to the dimmer Neutral?
And the parameters 21 and 22 should be:
21 = 1 for Neutral installation (as opposed to no neutral)
22 = 0 for single pole installation (as opposed to a 3-Way)
John