Backup & recovery

Nobody can reset a FEN account for you. There is no email address, no password, no support desk with a copy of your key — the key on your device is the account. That makes this the one chapter worth reading before you need it.

The short version: pick a saving folder that syncs off your phone, and let FEN keep your key backup in it. That is the whole safety net.

What FEN backs up

Two different things end up in your saving folder, and they cover different ground.

	What it is	What it holds
Key backup	fen-keys-backup.<account>.<device>.json, one per device	Your account key, every group key you hold, your backend settings, your friends list — no expenses
Closed-group archives	fen_group_<group>_<date>.zip or .fengroup	The full history of one closed group: every expense, settlement and receipt

The key backup is what puts your account on a new phone. The archives are what keep a closed group readable after the backend copy expires (about 30 days after closing).

Both are encrypted with your folder password if you set one — and the key backup carries that password inside it, so restoring re-establishes it without you having to set it again.

How often the key backup is written

Automatically, whenever what it holds could have changed:

• after every sync;
• the moment you create a group;
• the moment you join one;
• when you change your saving folder or its password.

It is only rewritten when the contents actually differ, so a synced folder isn't churning uploads. Each device keeps exactly one current file — restoring onto a new phone gives that phone its own, alongside the one you restored from. Two conditions gate all of it: a saving folder has to be configured, and Back up encryption keys has to be on — it switches itself on the first time you pick a folder.

:::tip The folder has to leave the phone A backup in a folder that only exists on the phone you lost is not a backup. iCloud Drive, Nextcloud, Proton Drive, Dropbox — anything that replicates. :::

Restoring onto a new phone

On the new phone's first screen, instead of typing a name, tap Add device with backup file and pick the key backup from your saving folder.

One file. There is one key backup per device, so if your old phone was your only one, you pick that one file. If you were running two devices, select both — each may know groups the other doesn't, and FEN merges them. Files from two different accounts are refused rather than mixed.

FEN reads the file as it is and only asks for the folder password if it turns out to be encrypted, and shows you what the file describes — the account name, and how many groups and friends are in it — before it applies anything.

:::caution Check the confirmation before tapping Restore A folder can hold several backup files: one per device, plus one for any account created on that phone since. The name carries a short account id followed by a device id — fen-keys-backup.a1b2c3d4.9f8e….json — so files sharing the first id belong to the same account, and one with a different first id is a different account entirely.

If the confirmation says 0 groups, you have picked the backup of a brand-new account. Cancel and choose another file — nothing has been written yet. :::

After you confirm, FEN restores the keys and immediately pulls your groups from your storage backend, so expenses and balances come back with them. A backup file holds your keys, not your data — the sync is what brings the data.

What comes back

• Every group with a backend, whether you created it or joined it.
• Your account name, your backend settings and credentials, your friends.
• Your folder password, so archives and future backups stay consistent.
• Closed groups, from the backend if they were closed recently, and otherwise from the archives in your folder (see below).

What does not

• Local-only groups. A group created with no backend was never anywhere but the phone you lost.
• Anything the old phone never synced. An expense added on the day the phone went missing, with no sync since, is gone.
• Your saving folder choice. Folder access is per-device, so pick the folder again on the new phone — the same one, if you want your archives.

Your old phone also stays listed under Settings › Devices. Retire it there once you are up and running.

Closed groups from your folder

Closed groups are only kept on the backend for about 30 days. After that the archive in your saving folder is the record — and FEN reads those archives back itself.

Every time you open the Groups tab, FEN looks in your saving folder for archives it has not read yet, decrypts them with your stored folder password and loads them back as ordinary closed groups: the real expenses, balances and receipts, on the normal group screens. Each file is read once; after that the group is simply part of the app again.

A folder holding years of archives is worked through a few at a time rather than all at once, so the app stays responsive — if an old group hasn't appeared yet, it arrives on one of the next few visits to the Groups tab.

This is also what makes a shared folder work between two people's devices — or your own old and new phone. Point the new phone at the same folder, restore your account, and closed groups that no longer exist on any backend come back from the files.

If an archive cannot be read, the Groups tab says so and names the file:

What it says	What to do
…is encrypted and no folder password is set on this device	Set your folder password in Settings › Profile — the same one the archive was written with.
…could not be opened with your folder password	The archive was written under a different password, or the file is damaged. Set the original password.
…belongs to a group whose keys are not on this device	Restore your account backup first; the archive is encrypted with that group's keys.
…is not a readable FEN archive	The file is truncated or is not a FEN archive at all.
…is far too large to be a FEN archive	Something else in the folder is using FEN's naming. Move it elsewhere.

:::danger Deleting a group deletes its archives too An archive is encrypted with the group's keys, and ⋮ › Delete group destroys them — so the file could never be opened again by anyone, including you. Deleting the group therefore deletes its archives from your saving folder as well, rather than leaving unopenable files behind.

Close a group you want to keep. Delete only what you want gone for good. :::

Using two devices at once

FEN has no server arbitrating between your devices, so two phones signed in to the same account can each record a different version of the same expense, and neither will show both.

Restoring is designed for replacement: restore onto the new phone, then stop using the old one. If both do end up writing, FEN shows a divergence warning at the top of the Groups tab and on Settings › Devices, naming the devices involved. It is a warning, not a lock — the fix is to pick one device and stop using the other.

A shared saving folder is not a way around this. It replicates your backups and your archives, not your live groups.

If you have no backup

The groups you joined that someone else created still exist on their storage — but your key was the only thing that could read them, and it was on the phone. Ask the organiser to invite you again; you will come back as a new member, with the group's history from the point you rejoin.

Anything that existed only on your device is gone. That is the cost of nobody else holding your key, and it is why the saving folder is worth setting up on the first day.