The best instructions for setting the RASA_PRO_LICENSE environment variable are at https://rasa.com/docs/rasa-pro/installation/python/licensing .
A couple of things could be happening here:
- You could have an older license that is expired; when did you get it?
- Are you using the correct set command for your environment? (Linux, Mac, Windows, …)
- More on JSON Web Tokens at https://jwt.io/introduction/.