The reason for moss is poor drainage or shade. Treat the poor drainage by 'spking your lawn first, as deep as you can with a garden fork, and if your are up for a challenge (? ) brush a couple of bags of course sand into the holes you've spiked. If the lawn is in mostly shade all day. it will never be a lawn. Put playbark down and build a climbing frame; add lighting, paint the fences and lay a patio with a sail over it