Manually start caddy from a terminal window not as a service.
Then any Caddy errors are show on the terminal.
Note the clipboard API which is used by the new version of Manager needs https not http access to work on a web browser. Manager does not natively provide https access, which is why I run Caddy. See
Bug with "Copy to Clipboard" - #69 by Patch For testing you can access Manager server from a web browser on the same computer for which htpps access is not required for clipboard API functionality, http is OK.