If you cannot install packages via the repository, the most reliable "verified" way is through the browser.
You run a small, lightweight Bitlbee server on a modern PC, a Raspberry Pi, or a cheap cloud VPS. This server handles the modern Facebook MQTT/Graph API connection. It then translates your Facebook messages into a standard IRC (Internet Relay Chat) feed that your Nokia N800 can easily read. Step-by-Step Setup: facebook messenger for nokia n800 verified
If you are seeing a message on your device asking you to "verify" your Facebook account, it is highly likely a . Do not click any links or provide your password. How To Check If Someone Logged In To Your Messenger Account If you cannot install packages via the repository,
Connect to a public BitlBee server, or host your own on a local Raspberry Pi to handle the modern TLS encryption requirements that the N800 struggles with. It then translates your Facebook messages into a