422 Error with @jwt_required() in Flask App Deployed on VPS with Nginx

Hi everyone,

I'm facing an issue while deploying my Flask application on a VPS server with Nginx. The app works fine when tested locally and also when hosted on Heroku. However, when deployed on my VPS, any route protected by @jwt_required() throws a 422 error.

Details:

• Server Setup:

  • Ubuntu VPS
  • Nginx as a reverse proxy
  • Gunicorn to run the Flask app
  • Flask-JWT-Extended for JWT authentication

• What Works:

  • All API routes without the @jwt_required() decorator work perfectly.
  • The same application works as expected (even with @jwt_required()) when deployed on Heroku.

• What Fails:

  • Any route using the @jwt_required() decorator on the VPS setup returns a 422 error.
  • Removing @jwt_required() allows the routes to work normally.

Things I’ve Tried:

• Verified that the JWT token is correctly passed in the Authorization header.
• Checked for mismatched SECRET_KEY and token expiration settings.
• Confirmed that the app uses the correct ACCESS_TOKEN_EXPIRES and ALGORITHM.
• Tested with Postman and curl—no difference.

I suspect it might have something to do with Nginx or Gunicorn configurations, but I can’t figure out what. Could it be related to how headers or JSON bodies are being handled by the server?

Any suggestions or troubleshooting tips would be greatly appreciated!

Thanks in advance!