# backup-format-unknown

A part of the backup has a **format version** that this version does not know.

- **Route:** `restore-backup`
- **Description:** `backup format is unknown: expected a backup item of version 2, or a backup that v1 wrote, which has no backup item`
- **Details:** **`part`**, the place of the part in the backup, counting from 0, with the full backup as part 0, and **`value`**, the `formatVersion` as the part gave it, as a number; without `value` if the part names no version.

## Why It Happens

Each part of a **[backup](/docs/eventsourcingdb/backup-and-restore)** that the v2 API created begins with a `backup` item, whose **`formatVersion`** names the version of its format. This version of EventSourcingDB creates and restores **version 2**. It also restores a backup that the v1 API created, which has no `backup` item and so names no version. A `backup` item with **another version, or without one**, is refused.

Another version comes from a backup that a **newer version of EventSourcingDB** created, or from a `backup` item that was changed by hand.

## How to Fix It

Restore the backup with the version of EventSourcingDB that created it, or a newer one. EventSourcingDB has removed what it restored so far, so the database is empty again. Resending the request to this version fails the same way.

## Example

For a restore whose full backup names the format version `3`, EventSourcingDB answers with this error, as a line of the stream, and then ends the stream with its `end` item:

```json
{
  "type": "error",
  "data": {
    "code": "https://docs.eventsourcingdb.io/errors/backup-format-unknown",
    "description": "backup format is unknown: expected a backup item of version 2, or a backup that v1 wrote, which has no backup item",
    "details": {
      "part": 0,
      "value": 3
    }
  }
}
```