For switching the production server to live mode, the following steps have to be done:

1. Change Paypal and Micropayment configuration in app/config/config.prod.json. Change the return URLs from spenden-2.wikimedia.de to spenden.wikimedia.de
2. Change the NGINX configuration in /etc/nginx/sites-available/spenden.wikimedia.de:
   1. Set domain from spenden-2.wikimedia.de to spenden.wikimedia.de
   2. Change the SSL certs, comment out the wildcard cert and insert the real cert (I've copied the cert files from the old server)
   3. Restart nginx
3. Change the DNS entry for spenden.wikimedia.de to point to the new server IP.