A developer runs `claude` for the first time and is immediately prompt — Claude Code Certified Professional Practice — Claude Cert Academy

A developer runs `claude` for the first time and is immediately prompted to authenticate. After completing OAuth they get a "session not found" error on the next command. What is the most likely cause?

• The Claude Code binary is corrupted and must be reinstalled
• The OAuth callback URL is blocked by a corporate firewall, so the token was never stored
• The developer used --no-auto-update and the binary version does not match the API
• The session cookie expired within the 60-second window before the next command

Answer: The OAuth callback URL is blocked by a corporate firewall, so the token was never stored

OAuth relies on a redirect to localhost; corporate firewalls or strict network policies that block loopback connections will prevent the token from being written to disk, causing a "session not found" error on the next invocation. Reinstalling would not help because the network issue persists. Version mismatch produces a different error. Tokens do not expire in 60 seconds.

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