I have executed:
$ heroku login
But when I try to push, I\'m still asked for authentication:
$ git push heroku master
Usern
This topic is old, I know.
However, none of the previous solutions worked for me.
My problem was that "Windows Credentials" (os: Windows 10) had another credential previously associated with Heroku (company account) and used this instead of the new one (my personal account).
I had to go to: "Control Panel\All Control Panel Items\Credential Manager" (from Control Panel), and modify all the credentials: https://git.heroku.com (and all those associated with "heroku" word) with the account current.
However, the password I placed the Key API that is displayed in "Dashboard" of the site and the command works: git push heroku master.
7 hours that life will not give me back. :/
My 2 cents.