Dig Box Help Please

Hello everyone,
I'm super new to owning a beardie, I got mine towards the end of February and I think we've been doing a good job of taking care of her/him. S/he's grown a lot and does poop almost every day, and doesn't seem to be stressed. But lately, our little beardie has been hiding in his/her fake rock cave digging away. We use paper towels to line the cage as it's easier to change and clean as his/her poops are daily and gigantic, but now beardies scratching and tearing the paper up and just scratching away and kind of just lays there in the rock cave with the shredded paper. I tried to make a dig box using a shoebox and some coconut shredded bedding but Beardie was uninterested and ran away from the box. Can anyone give me any idea as to what other substrate I can, or should be using. Or anything I can do to help my little buddy with the scratching?

LAYBOX
potting soil that doesn't have any type of
chemicals or fertilizers in it, mixed with sand, etc. Be sure it is at least 10-12 inches deep & that
the mix is damp enough to where it will hold up to her making a burrow but not sopping wet to
have standing water.

Thank you so much! Is there a specific kind of sand I should get?

Play sand

Thank you so much!!