macosmacOS 12.1 , custom smbSMB port, i
I was getting the same 'Authentication"Authentication error (80) - the correct user or password info may not exist in the System.keychain or the server may no longer allow access for this user.'"
itIt was ana keychain issue, after. After adding the location i, I looked in Keychain Access and the Time machine location, at 'where' it was saved as smb://server/foldersmb://server/folder
instead of smb://server:port/folder, sosmb://server:port/folder
So I added the port and it works now.