Importing Sharepoint pages in QnA Maker knowledge base not working

I'm trying to import Sharepoint pages in a QnA Maker knowledge base as URL but without success. Every time obtaining a:

Bad Argument
Unsupported/Invalid URLs: "https://myapp.sharepoint.com/sites/AllKeyServices"

I've read the documentation here but it was not helpful.

1. The Sharepoint is not public
2. The account I'm usig when adding the URL is enabled to access sharepoint
3. When clicking on "Save and train" the authentication popup appears (really fast indeed, I cannot see what's inside, but I think it is the token request successfully execute. So I think it should not be the same case of this)
4. If I save the page as PDF and import it as file, it works.
5. It's not some file on SharePoint I want to import, I need to import the page itself.

Any idea on how to understand what's wrong?
Page formatting? Should not, due to 4)
Permission? Should not, due to 3)
What else?

I found this documentation page that states:

"SharePoint resources must be files, not web pages."

so, it should be a wanted/known limitation (quite weird, indeed).