You can't just cobble random bits together.
You are trying to control a Mercury Vapor light with a dimmer
That doesn't work.
I know you are thinking of that unit as a "smart switch", but it is plainly a dimmer. As a general rule, if a switch is a powered switch (lighted switch, motion sensor, smart switch, dimmer, etc.) that does not have a neutral wire, it is special, and must not be connected to anything except a) an indandescent, or b) LEDs listed and labeled for dimming. The reason is the bulb itself must allow leakage current through the bulb, to power the switch itself.
You certainly never hook any dimmer or powered switch to a discharge light... Those include the fluorescent*, neon and HID families, HID includes low pressure sodium, high pressure sodium, mercury vapor, and metal halide. All these have have very, inductive ballasts, which do not like having their power supply limited, and will make every effort to set the dimmer on fire.
To smart-control this light, you must find a smart switch specifically listed and labeled to control HID lighting, has a "ballast rating" within your ampacity (2.0 from the label x 2 = 4.0A), and takes a neutral wire. If you ever figure to upgrade this light to LED, also lok for one with a "tungsten" or "LED" rating for whatever your LEDs will draw (about the same, I would think).
* It's possible to get dimmable fluorescents but they use unusual control systems, not run of the mill Home Depot dimmers. I've never heard of dimmable HID, except in the "indoor horticulture grow light" business, who are the only people still advancing HID technology.