Sync WebDAV to ugreen nas error: "Webdav_error Not authorized"

Hi, I can't get WebDAV to work. Here is what I did:
(1) I have a Ugreen NAS, enabled WebDAV for http and https. Tested in browser and working fine. Ugreen does not provide tokens. Login with username and password.

(2) configured OSS Documents:
configured http:
server address: http:// :5005/
username, password (user is nas adming with full access)
remote folder: /volume2/live/
==> Test is successful (green)
==> https is not working
(3) on Documents page I push the sync button, after 2 seconds I get "Webdav_error Not authorized"

Could anyone help please ? I tried every permutation of combinations I could think off. It is the first use of WebDAV for me and I am not very experienced. Any help is appreciated.

What I am wondering:

• why isn't the password saved in the config page ? Is this the problem. No password entry is coming up when
  syncing
• why isn't https working in config page ? I am fine with http (all inside my home network), just wondering what the
  problem could be.
• in the documentation I have read that Google Drive is supported, but in the app I only see options for WebDAV
  and for local folder ?

Thank you very much for your time and support

Start at the WebDAV configuration page and the Documents-page sync action, then reproduce the Ugreen NAS HTTP case and capture the authorization failure. Check the credential-saving, HTTPS, and provider-support questions separately; done means identifying a confirmed cause and documenting or fixing the affected behavior.