remote: repository not found fatal: not found

Three things:

1. Your GitHub username is not an email address. It should be a username (like "sethvargo")

2. You have a trailing slash on your repo name:

   $ git remote rm origin
   $ git remote add origin https://github.com/pete/first_app.git
   

3. You need to create the first_app repo. I looked at "pete" on GitHub, and I do not see the repository. You must first create the remote repository before you may push.

If this problem comes on a Windows machine, do the following.

• Go to Credential Manager
• Go to Windows Credentials
• Delete the entries under Generic Credentials
• Try connecting again. This time, it should prompt you for the correct username and password.

Your username shouldn't be an email address, but your GitHub user account: pete.
And your password should be your GitHub account password (2014).

Update 2021: your password should be (since Aug. 2021) a PAT (Personal Access Token).

You actually can set your username directly in the remote url, in order for Git to request only your password:

cd C:\Users\petey_000\rails_projects\first_app
git remote set-url origin https://[email protected]/pete/first_app

And you need to create the fist_app repo on GitHub first: make sure to create it completely empty, or, if you create it with an initial commit (including a README.md, a license file and a .gitignore file), then do a git pull first, before making your git push.