It's only January..........there are a good 2-3 more months of relentlessly wet weather on the horizon so treating for the moss now will only mean you will have to treat again when the rainy season tapers off. Most experienced PNW'ers wait :-))

When you do treat, something like Lily Miller Moss Out for Roofs and Walks works perfectly well and is environmentally safe.

Moss and algae growth over winter on various surfaces is a PNW fact of life. It's wet here and with very little actual sun to deter their growth. This is something that you will need address on an annual basis.

Or just give up and enjoy your mossy surface....you know people DO try to cultivate mosses for that.

It’s not meant to be a mossy platform walkway or garden...It’s a sport court for
Bball