Without knowing much about your configuration the most likely issue is that you haven't set a proper hostname nor have you generated a valid ssl certificate which.
Generating certificates directly for Ip's such as yours (https://143.198.26.153) is something that's currently being integrated in i.e letsencrypt.
I would suggest instead of looking at guides you linked you should check the official documentation of ownCloud for installing: https://doc.owncloud.com/server/next/admin_manual/installation/.

The Quick install guide provides you with instructions to properly configure a hostname for your own cloud instance.
There are also different ways to setup SSL certificates: One way is to import them directly through the web interface, another one would be to use the Mozilla SSL Configuration Generator (which the wiki also mentions), the last way would be to run a reverse proxy such as Nginx which would (with the right configuration) handle the https traffic for you.