In latest beta I was adding a new Kodi host. It finds it with the correct web host port. It will not add the host because it does not have proper user credentials yet. It does the same thing under manual entry. It tries to check for successful connection as it should but it cannot connect without credentials in Kodi and offers no way to enter them without adding host first.
Please as the template ask provide logs and more details like the error message you get.
The credentials fields are visible when needed, your issue is not a credential issue but probably a port used by something else or firewall issue.