Radarr/Radarr · error · UnsupportedMediaTypeException

Invalid extension, must be one of: {ValidExtensions.Join(",

Error message

Invalid extension, must be one of: {ValidExtensions.Join(", ")}

What it means

Thrown as an UnsupportedMediaTypeException (HTTP 415) by the POST /api/v3/system/backup/restore/upload endpoint when the uploaded multipart file's extension is not in the hardcoded whitelist {".zip", ".db", ".xml"}. Radarr only restores archives in the three formats its own backup writer produces. The check at BackupController.cs:106-110 uses Path.GetExtension(file.FileName) (which includes the leading dot and returns "" for extensionless names) tested with List<string>.Contains, a case-sensitive comparison, so an uppercase extension like .ZIP or .Xml also fails.

Source

Thrown at src/Radarr.Api.V3/System/Backup/BackupController.cs:110

        }

        [HttpPost("restore/upload")]
        [RequestFormLimits(MultipartBodyLengthLimit = 5000000000)]
        public object UploadAndRestore()
        {
            var files = Request.Form.Files;

            if (files.Empty())
            {
                throw new BadRequestException("file must be provided");
            }

            var file = files[0];
            var extension = Path.GetExtension(file.FileName);

            if (!ValidExtensions.Contains(extension))
            {
                throw new UnsupportedMediaTypeException($"Invalid extension, must be one of: {ValidExtensions.Join(", ")}");
            }

            var path = Path.Combine(_appFolderInfo.TempFolder, $"radarr_backup_restore{extension}");

            _diskProvider.SaveStream(file.OpenReadStream(), path);
            _backupService.Restore(path);

            // Cleanup restored file
            _diskProvider.DeleteFile(path);

            return new
            {
                RestartRequired = true
            };
        }

        private string GetBackupPath(NzbDrone.Core.Backup.Backup backup)
        {

View on GitHub (pinned to ca451608dc)

Solutions

Rename the file so its extension is exactly one of .zip, .db, or .xml, all lowercase (e.g. mybackup.zip).
If the file is a .tar.gz or other archive, repackage it as a .zip before upload.
Confirm the extension is truly lowercase by checking with `ls` or `dir`; macOS/Windows 'hide extensions' can mask a .ZIP rename.
If you genuinely need a new backup format supported, add it to the ValidExtensions list in src/Radarr.Api.V3/System/Backup/BackupController.cs:23 and ensure _backupService.Restore can parse it.

Example fix

// before: uploading radarr_backup_2024.BAK -> 415 Invalid extension
// after: rename the file and re-upload
cp radarr_backup_2024.BAK radarr_backup_2024.zip
curl -X POST http://localhost:7878/api/v3/system/backup/restore/upload \
  -H "X-Api-Key: $API_KEY" \
  -F "file=@radarr_backup_2024.zip"

Defensive patterns

Strategy: validation

Validate before calling

// Client-side: check the file extension before posting
var allowed = new[] { ".zip", ".db", ".xml" };
var ext = Path.GetExtension(filePath).ToLowerInvariant(); // mirror the server's lowercase whitelist
if (!allowed.Contains(ext))
{
    throw new InvalidOperationException(
        $"File extension '{ext}' not supported. Allowed: {string.Join(", ", allowed)}");
}
// then upload
using var form = new MultipartFormDataContent();
using var fs = File.OpenRead(filePath);
form.Add(new StreamContent(fs), "file", Path.GetFileName(filePath));
var resp = await client.PostAsync("api/v3/system/backup/restore/upload", form);

Prevention

Always download backups directly from a Radarr GET /api/v3/system/backup response and restore them unchanged so the extension matches the whitelist.
Use Path.GetExtension (not a string EndsWith) when validating, to exactly match the server's logic.
Lowercase the extension client-side because the server's List<string>.Contains is case-sensitive.
Avoid renaming backups through GUIs that hide extensions; verify with ls/dir before upload.

When it happens

Trigger: Uploading a backup file with no extension (Path.GetExtension returns ""), a wrong extension (.bak, .tar, .7z), or a compound extension where only the last segment is inspected (.tar.gz yields ".gz"). Also any uppercase variant such as .ZIP, .DB, .XML because List<string>.Contains is ordinal/case-sensitive and the whitelist is all-lowercase.

Common situations: Restoring a backup downloaded from another Radarr instance that was renamed during transfer; restoring a manually zipped archive produced by a different tool; OS-level 'hide extensions' settings causing a user to append .zip to a file already named .zip (producing .zip.zip, which still passes); cross-platform restores where the file got a capitalized extension through a GUI rename.

Related errors

AI-assisted analysis of Radarr/Radarr@ca451608dc (2026-08-13). Data as JSON: /api/errors/c834265ca6637831. Report an issue: GitHub.