Error 6740: The machine was not reachable.
The only error is a certificate issue.
The default website has stopped.
When restart get an error: Another website might be using the same port.
I can load ArcGIS Server Admin/Manage
The status is started, but not reachable, when launch the REST URL.
I opened arcgis/admin
Then opened the Webadaptor details, saw the port number was 80 not 443.
I found an article that provides information to update the Port number, will try this