Azure AIP Scanner - Set-AIPAuthentication Error

I am setting up Azure Information Protection Scanner and following the following support articles

Deploying the Azure Information Protection scanner to automatically classify and protect files

Admin Guide: Using Powershell with the Azure Information Protection unified client

As part of my AIPScanner set up, I first installed the Classic AIP Client, then Installed the Scanner (Install-AIPScanner), then Set up 2 applications (OnBehalfOf and AIP Client). 

I am now at the part of the Admin Guide: Using Powershell with the Azure Information Protection unified client support article to set up AIP Authentication using the Set-AIPAuthenication cmdlet. However, when I run the PowerShell cmdlets specified in the support article and listed below. I get the following error...

Set-AIPAuthentication : A parameter cannot be found that matches parameter name 'WebAppId'.

It appears that the Parameter WebAppID cannot be found.. 

The PS cmdlet I am using is as follows:

$pscreds = Get-Credential "user@Domain.com"
Set-AIPAuthentication -WebAppId "xxxxxxxx-xxxx-xxxx-xxxx-xxxx" -WebAppKey "x_xx_xxx_xxxx" -NativeAppId "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx" -OnBehalfOf $pscreds

Any ideas on what the issue can be?

Thank you

Pginnega69