Well, one scenario is your friend lied to you and he’s not litter box trained, haha. BUT! There are definitely some things you can do to encourage litter box habits.

If there are locations where Cotton typically uses the bathroom, relocate the litter box there. Rabbits naturally pee/poop in the same place, in addition to where they eat, which is why almost everyone puts hay in litter boxes.

It seems Cotton has not identified the litterbox as the bathroom, so you’ll need to let him know that’s where it is. You need to watch his bottom pretty attentively (I found myself literally ear on the floor, watching Wick’s bottom for an absurd amount of time some days…) and once he has an incident outside his litterbox, pick him up, along with the poop, and carry him and the poop to the litterbox. Once he’s in, pet him while he’s in there. If there are any situations where he poops in the litterbox, immediately praise him like crazy. Never use treats as a reward though, because your rabbit could think pooping will result in a treat (which is a bad association, haha).

For peeing, although it’s gross at first, I would tear the urine-soaked portion of the paper towel I used to wipe up Wick’s messes and plop them in the litterbox. Same procedure as pooping, I’d pick him up and plop him in the litterbox if he peed (sometimes I get him mid pee so I get it on me, but that’s the price I pay for training). Also clean up pees immediately so Cotton realizes only his litterbox will be the pee-palace. If you can catch Cotton right before he pees (his bottom assumes the position but the urine has not exited yet), try and get him over to the litter box, then once he pees, praise him again.

As for the actual litter, I used paper balls (Kaytee small granule blend). I have no experience with rabbits preferring one litter over another, so not sure if ratio/material affects it drastically.