It's sometimes hard to tell baby bunnies males from females! We spent about an hour picking out Acacia 5 years ago bc we needed a female. Males keep it tucked inside, if you know what I mean!!
Anyway, a vet will tell you the best path to take. If it's a female, have her spayed as soon as you can. If it's a male, I would have him neutered bc male pee spray is a far worse (and grosser) problem than a piddle on the couch!!
The litter in the cage is also used as a bed? That could be the problem. He might not be litter trained at all. A bunny should never use his pee area as a bed!! How big is the cage? And is the litter separate from the bedding? To reduce confusion, the litter box substrate should differ from the cage liner and bedding substrate. Paper pellets or kiln dried kitty pine are good for pee box litter. While something softer like fleece is a preffered bedding
As Sasami stated as well, bunnies just like to pee on soft things sometimes. I NEVER have a problem with Acacia unless she's on our bed for too long. And "too long" to her is like 10 minutes. She's perfectly litter trained everywhere else. Silly buns!!
An important note to make, never scold your bunny for peeing on the couch or for anything. Harsh language and sharp voices can penetrate your bonding process. Bunnies are sensitive, and they don't pee to be manevolent! They just don't know.
To get the smell and stain off the couch (and to increase the chances of him not doing it over and over) pick up some Nature's Miracle. It's enzymatic formula breaks down odors and stuff in the fibres of the couch