Hey,
We are doing this using the Library/Powershell/Invoke an external script. We found that the vCo service account needs to connect to SCCM using powershell once and then it worked.
Login to SCCM server with vCo service account (this is the account configured under inventory\powershell\<SCCM server added as a PShost>)
Open SCCM and from the top left chose connect using powershell. this will prompt you to say yes to running scripts.
try running your script again.