Well, have you put any toys in the pen? And treats in it? Have you sat in it and see if he’ll come out? If you wanted, you can take off the petstore cage and just have it be the pen, of course with a couple of cardboard boxes( recommended because they are hidey houses but also great for buns to bunstruct them). But remember, when you bring a bun home, they need to be left alone for a week or so until they become acclimated to the house, then you can do what I sugested. Also, what are your floors? If they are slippery(not carpet) buns don’t like that and feel unsafe on it so they will avoid those areas.

I just got my first bunny ever yesterday so I doubt this will be helpful but we got all the supplies (cage, food, hay, etc.) from her old owner. There’s this area she can walk up to in her cage to be up a little bit from the ground. Although she’s almost always below it. I’m pretty sure it’s because she’s still brand new to us and were brand new to her, but she usually just sits there unless shes drinking her water, nibbling her hay, etc. I plan on getting her some toys today to see if that will motivate her to move around a little bit but I don’t expect it. From what i’ve been reading there’s a 50/50 chance bunnies even like to play with actual store bought toys and she’s new so she might not trust them. I guess i’m kind of just summarizing the person above me. Just try and give him some toys or treats and maybe he’ll start to adjust. But I’m a new Bunny Mom so I honestly have no clue what will turn out.