Do some digging around on google, as moss is in its own world. Basically moss is everywhere and you have to change its growing conditions. Think of moss as a weed. Grows everywhere and a pain to get rid of. To get under control, there are several products available at big box hardware stores. And it takes longer than what I thought it would take. Then once under control make sure to the maintenance to keep it under control. I have about 1/4 of my roof that never see daylight so lots of moss. Once under control I sprinkle powered laundry soap about 3 times a year to keep under control. Liquid dish soap spray'd out of a garden sprayer also helps. Or spend the money and install zinc strips. But they are somewhat hard to put or keep in after roof has been installed. Atleast mine.
I also do my rv with dish soap. I open up awning and spray it and roof and let it soak for awhile then hose off.
I used to use a pressure washer. Not anymore. If you do, use largest angle head you have. I use a 40 degree and don't let spray hit with much pressure. But may problems with pressure washer.
1. Gets slippery and you're up on the roof.
2. Dragging hose around make black marks when hose comes over edge.
3. Get to close with spray and you've just added to your problems, not solved them.
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"