As described earlier install certbot
HTTPS with LetsEncrypt and nginx Rename certbot fullchain.pem and privkey.pem to fullchain.txt and privkey.txt Upload using HostEurope KIS Webinterface
Produktverwaltung – Webhosting – Konfigurieren – Sicherheit & SSL – SSL administrieren

Wait 1-2 mins – voila, certificate renewed and validate Based on:
https://danielpietzsch.com/articles/he-ssl