Deploy with git to dokku on digitalocean

I' trying to push my first app on digitalocean with git. on the server there is an instance of dokku installed.

I tried this Tutorial: http://ift.tt/1sRIQBP

BUT when I try $ git push dokku master , it says:

fatal: 'testapp' does not appear to be a git repository fatal: Could not read from remote repository.

Please make sure you have the correct access rights and the repository exists.

I really can't find a soloution.