I am really looking forward to using Outline for work, however, I am having trouble getting WebDAV to work. It keeps responding with Wrong Credentials - Expected status code in (200-499), got 501. Note that I can get this same set of credentials and URL to work through other (lesser) apps. Honestly, this is the only thing stopping me from pulling the trigger on both the iOS and the Mac.
I did notice that you seem to be looking for a domain/user format where I just have a username (in the form of an email address).