Could a firewall be blocking the connection? How do I check?

Yes, a firewall is a common culprit. Check your system's firewall (e.g., `ufw` on Ubuntu, Windows Firewall) to ensure that outgoing connections to api.telegram.org on port 443 are allowed. Temporarily disabling the firewall (for testing purposes only!) can help determine if it's the cause. If using a network firewall, consult your network administrator.