Getting Lighter Pro back
Lighter Pro is a one-time purchase, tied to the Apple Account you bought it with. On a new iPhone, or if Lighter doesn’t show Pro, open Lighter’s Settings and tap Restore Purchases, under Your plan.
Syncing across devices
iCloud sync is off until you turn it on. On each iPhone, sign in to the same Apple Account, then turn on iCloud sync in Lighter’s Settings, under Sync & export. It starts the next time you open Lighter.
Sync keeps your iPhones in step; it isn’t a separate copy.
Keeping a copy of your journal
In Lighter’s Settings, under Sync & export, tap Export journal and choose PDF, Markdown or plain text. Save the file wherever you like.
Removing everything
Delete Lighter from each iPhone. If iCloud sync was on, delete Lighter’s data from iCloud too: in the Settings app, tap your name, then iCloud, then your storage at the top, then Lighter, and delete its data there.
If your iPhone backs up to iCloud, its last backup may still hold Lighter’s data until the next one replaces it.
The one thing that stays is a note in your iPhone’s Keychain that you own Lighter Pro, so a reinstall still has it.