Email info@crindustries.xyz
Tell us what happened, what you expected instead, and which device and OS version you were on. If the app closed unexpectedly, sending the crash report from Settings, then Privacy and Security, then Analytics, is far more useful than a description.
Sync runs through your own iCloud, so start by checking that the device is signed in to the same Apple Account and that iCloud Drive is on. A device that has just been restored or freshly signed in may still be pulling the library down. If a note is still missing after that, email us before you edit anything on either device, because the state at the moment it went wrong is the useful thing.
Use Restore Purchases in settings. Entitlements are tied to your Apple Account, so this works on any device signed in to it, including after a wipe. If it does not, email us with the Apple Account you bought it with.
Import reads a file you choose and writes into your library on the device. It is safe to run twice: re-importing the same export updates what is already there rather than creating duplicates. Every import finishes with a report telling you what came in, what was changed on the way, and what could not be read. If that report says something was dropped and you need it, send us the report rather than the file, since the file is your notes.
Everything exports as plain Markdown with its attachments. This is not a courtesy feature and it is not going behind a paywall. If export ever fails on your library, that is a bug we want to hear about the same day.
Send them. It helps to say what you were trying to get done rather than the feature you had in mind, because the first one is usually solvable in a way the second one is not.