Hi @ArttuHer ,

• First of all check the scopes of your personal access token.
  Go to github/settings/Developer Settings.
  When the token is created, you need to define what permissions are granted to the token.
  Make sure repo scope is selected:

• Make sure you have write access to repository. Just because you are able to pull from a public repository doesn't necessarily mean you have write access. Are you the owner of the repository or have you been added as a collaborator? Can you make the changes to the code directly in github?