Instead of guano to help entice our bats we used a bat attractant spray that smells like bat pee.
This article might help- Bat Attractant: The Secret Weapon For Bat House Success
We were also told to turn it upside down and fill our bat house up with dirt and leave it for a few weeks becasue apparently the bats don't like the smell of the newly cut wood used to make the box. We did this before adding the attractant. Not sure if it was one or both of these that worked but we did have bats move in shortly after hanging it.