Unregister non-existing server site

[Thomas_HvassKristensen]

I need to unregister a non-existing ArcGIS Server site in from the Portal. However using the unregister url I found in another thread gives me:
https://<portalhost>/portal/sharing/rest/portals/0123456789ABCDEF/servers/<siteID>/unregister 

Error

You do not have permissions to access this resource or perform this operation.

Error: 403

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I'm logged in as Portal Admin, and this is Version 10.7, and I have tried both through the Webadaptor and directly on the Portal Host.

Thanks

[liqiuping]

you have to use the "post" method and a "token" should be added in your data before you post it.