Store your notes in iCloud Drive. Notes in iCloud Drive sync to every device signed in with your Apple ID.
Step 1: Switch the storage to iCloud Drive
At the bottom of the sidebar on the home screen, switch from On My Device to iCloud Drive. The first time, CollaNote explains how it works; tap Use iCloud Drive.
Step 2: Bring your existing notes over
On My Device and iCloud Drive are two separate folders that do not share notes. Use Move or Copy to bring the notes you want into iCloud Drive.
Step 3: Do the same on your other devices
Open CollaNote on your other iPad, iPhone or Mac with the same Apple ID and choose iCloud Drive there too.
Make sure iCloud has enough free space, and back up your notes before you turn iCloud off. If CollaNote says it can't select the iCloud folder, turn on iCloud Drive in the Settings app first.