The account is uploaded and does nothing. There are exactly four causes, and they differ in what the system reports.
1. Mismatched file pair
You need two files with the same base name: phone.json and phone.session. A session from one account with a json from another will never connect — the json carries the app parameters the session was created with. Check that the names match before the extension.
2. The proxy is not answering
The most common cause. A proxy can be alive for a browser and dead for Telegram: different protocol, different ports. The symptom is a connection that hangs and times out rather than failing instantly. Test the proxy separately and confirm it is socks5, not http.
3. The session is invalid
The account was logged out — manually from a phone, by a password change, or because Telegram terminated all sessions. Here the system says so directly. Only re-authorisation fixes it; the file cannot be repaired.
4. The account is banned
Connection succeeds and every action bounces. A status check shows a ban or a deletion. That is the end of the road: appeals exist for spam restrictions, not for bans.
Order of checks
Status first — it is free and answers half the question. Then the proxy. Then the files. Changing everything at once tells you nothing and guarantees you repeat the mistake on the next account. What protects accounts in service is on the automation page.