Appveyor

• In case of organizations, public project membership on GitHub at https://github.com/orgs/<orgname>/people/<username> is required
• Sign up with the username or organization name on GitHub
• Revoke GitHub access if the project is owned by another account
• Reauthorize if revoked
• Create a Personal access token with repo permissions
• Encrypt the token
• Add the encrypted token string to the configuration file

Source: Publishing artifacts to GitHub Releases