Yay, welcome new bunny owner to our forum
This forum is a treasure trove of good advice from long-time bunny owners.
Rabbits can definitely be litter trained, as they’re creatures of habit. A habit can be difficult to un-learn and replace with a new habit, but gentle encouragement and being patient helps.
We had the same problems with our bun, and we got some great advice which you can see in this thread: https://binkybunny.com/FORUM/tabid/54/aft/146503/Default.aspx
Breintje has been doing well ever since. There were some slip-ups, because we had a corner-model litter box. Since we got him a large rectangular litter box (which actually was the lower lid of a muffin carrying tray) things have improved drastically. Our bun became so well-adjusted to this new situation that a year later we recognised a health issue as soon as it came up. He was peeing outside of the box, and this was our cue to take him to the vet ASAP. He seems to be doing well now.
This is important info for new rabbit owners: they really are creastures of habit. Watch these closely, gently try to replace unwanted habits, and keep an eye out for sudden changes in their habits as they might indicate health issues. Living together, and learning each others’ ways and habits will greatly improve the bond between you and your bun. They are such wonderful animals, and they will really form an emotional bond with you. Having a bad day? Many people here have found that their buns actively sought them out to comfort them. Wonderful, isn’t it?