Okay I thought you were using alexaPi, looks like alexa-client. In that case, have you run
cd /home/pi/MagicMirror/alexa-client/
pip install -r requirements.txt
python setup.py install
sudo pip install -r auth_web_requirements.txt
already? If so, try
cd /home/pi/MagicMirror/alexa-client/
python auth_web.py
In this application you will need to add the token you get from the website to your settings.py file. After you get the token, run nano settings.py and paste the token where it says
REFRESH_TOKEN= ``
so it will say something like
REFRESH_TOKEN= `yourTokenGoesHere`