Of course these URLs are “well known” (to you and me)
For clarification, “well-known URIs” are a protocol DavDroid uses to detect the full DAV URL when only a hostname is given.
Using App Password as recommended
2018-11-26 18:22:16 703 [HttpClient] Incorrect username or password.
Seems to be saying my username and password are wrong?
Just tried again, copied the password directly from the fastmail app, copied into DAVDroid, tap the eyeball, made sure the password was correct, and it still didn’t work.
Tried with the URL provided here:
Both 4G and Wifi, no luck.
Seems like your user name / password is incorrect.
Did you try as described on https://www.davdroid.com/tested-with/fastmail/?
Did you use your full email address (without special characters like " " from copy/paste) as user name?
Did you use the generated app password (without special characters like " " from copy/paste) as password?
Is there any other way how we can help you? This is most probably not a DAVdroid problem.