This operation unfederates an ArcGIS Server from Portal for ArcGIS.
Unfederating a server site has several significant consequences and should not be done as part of routine troubleshooting. It is an act that is not easily undone and may have irreversible consequences. Only unfederate a site if you have a clear understanding of the impact. See Administer a federated server for more details.
The response format. Default is html.
Values: html | json | pjson
Below is a sample POST request for unfederate:
POST /webadaptor/portaladmin/federation/servers/FfURK2ysFiMjzDkJ/unfederate HTTP/1.1 Host: machine.domain.com Content-Type: application/x-www-form-urlencoded Content-Length:  f=json
JSON Response example