Content Manager uses a "Steam Bridge" to authenticate your account. If Steam is acting up, the server won't recognize you.
The most common cause of the "unavailable" error is a mismatch between your files and the server’s files. Assetto Corsa isn't always great at telling you why it failed. Content Manager uses a "Steam Bridge" to authenticate
Sometimes your PC sends too many requests to the server at once, causing the server to "ghost" you. Open . Go to Settings > Assetto Corsa > Online . Look for Frequency of updates or Network settings . Content Manager uses a "Steam Bridge" to authenticate