When I tested, it behaved only without the @ in username. I’d have asked you to file an issue, but I see
Parsing a .json configuration for WebDAV does not work #3619 which was closed as not reproducible.
Looking at it further, I think the difference is that the export without password export selected leaves @.
Looking at the TargetURL, this looks like how you ran. Does yours run OK if you export the password?