This administrative operation is not available when accessed through a Web Adaptor. This operation should be accessed using a direct URL to one of the GIS servers on the site.
The importSite operation lets you restore your site from a backup site configuration file that you created using the exportSite operation. It imports the site configuration file into the currently running portal site.
The importSite operation will replace all site configurations with information included in the backup site configuration file. See the exportSite operation documentation for details on what the backup file includes. The importSite operation also updates the portal content index.
This operation is computationally expensive and can run for a long time. Since this operation changes the portal site configuration completely, it is highly recommended that you do not access portal items or administer the site while the operation is running.
Token expiration when importing site
When using the import site operation to restore a backup, a token is generated that will expire after an hour. If your backup is taking longer than an hour to restore, the import process will fail. To circumvent this, generate a token using the Sharing API and specify the expiration time to be longer than the default. If you are accessing the Portal Admin Directory through a web browser, the token generated via the Sharing API should be appended to the import site operation URL. If you're calling the operation from a script, the new token should be included in the API call.
A file path to an exported configuration.
The response format. The default response format is html.
Values: json | html | pjson
Below is a sample POST request for importSite:
POST /arcgis/portaladmin/importSite HTTP/1.1 Host: machine.domain.com Content-Type: application/x-www-form-urlencoded Content-Length:  location=\\server\share\backup\Oct-06-2018_10-20-55.portalsite&f=json
JSON Response example