title: How to add flask cor module to work on Heroku?
body: <p>I have a problem when I try to use flask_cors in my flask app but when I deploy this app on Heroku so it fails and from the Heroku logs I have this error :</p>
  
  <p><code>from flask_cors import CORS, cross_origin 
   ModuleNotFoundError: No module named 'flask_cors'</code>
  I have added 'flask_cors' in the requirement.txt file but it's still no work. Thank you!</p>