Failed to login into my sendgrid account with Heroku's Username and password

 I had deployed my Rails project through Heroku. Recently, I decided to add mailer to that app and deployed the master branch. In order to send a email, I installed SendGrid add-on and followed the document which you can find in dev center. I set up SENDGRID_USERNAME and SENDGRID_PASSWORD. After that I tried to login but it didn't accept them. I don't quite understand what is happening here. If someone is experiencing same situation, please enlighten me how to solve this probrem.