Can't write to ROOTCIMV2TerminalServices via powershell

I’m trying to automate installing new SSL certificates onto a Windows Server using powershell. I have most of it done but I have a small issue. When I try to update the Terminal Services SSL cert I keep getting an error and for the life of me I can’t figure out why.

    $NewCert = Import-Certificate -FilePath $FileName -CertStoreLocation cert:LocalMachineMy
    $RDPInstance = Get-CimInstance -ClassName Win32_TSGeneralSetting -Namespace ROOTCIMV2TerminalServices
    $RDPInstance.SSLCertificateSHA1Hash = $NewCert.Thumbprint
    Set-CimInstance -CimInstance $RDPInstance -Passthru

I took most of this code from Microsoft’s site to be able to do this update but it throws the error:

    Set-CimInstance : Invalid parameter
    At line:1 char:1
    + Set-CimInstance -CimInstance $RDPInstance -Passthru
    + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        + CategoryInfo          : InvalidArgument: (Win32_TSGeneral...me = "RDP-Tcp"):CimInstance) [Set-CimInstance], CimException
        + FullyQualifiedErrorId : HRESULT 0x80041008,Microsoft.Management.Infrastructure.CimCmdlets.SetCimInstanceCommand

I have tried a few versions of the Set-CimInstance but all of them seem to throw the same Invalid parameter.