My chickens refuse to sleep in their Omlet Cube coop — should I just return it?

I got my first 3 chickens about three weeks ago. On their first night, I put them inside the Omlet Cube and closed the door.

Since then, they have never gone back inside on their own.

They free-range during the day and, when evening comes, they prefer sleeping perched in bushes/trees instead of going into the Cube.

It's been three weeks now, so I'm starting to wonder whether they'll ever use it. 😅

Has anyone had the same problem with an Omlet Cube? Did your chickens eventually figure it out, or should I just accept that they prefer sleeping outside and return the Cube?

Any tips for getting them to use it would be appreciated

Peace