Why doesn't my budgies use their nest box?

I have two budgies, male and female, and are both age appropriate for breeding. They are bonded, and i inserted a nest box so they can breed. It's been there for a couple days, and my momma bird or papa bird hasn't touched it one bit. I put some tissue inside, for coziness. There's a cavity on the bottom, so it's safe. They stay away from the box. And it's breeding season! Is anything wrong? They are all healthy too!