Failure to link user/ext with API

I am trying to automate the process of linking a PABX user to an extension using /rest/dialplan/link/

Below is the parameters I am passing into the API:

The resulting output is returned:

*Result:  fail*
  • Message: no permission to link extension*
  • Values:*

The token I am feeding in is attached to a user who has system-administrator permissions and with the same user account I am able to use the Web-UI and link extension and user together.

Any thoughts/input would be greatly appreciated.

Many thanks,