Data Refresh API error in PowerShell

Hello,

I'm getting the following error when using the sample code in GitHub. 

Invoke-RestMethod : The remote server returned an error: (415) Unsupported Media Type.
At C:\Users\user\Documents\GitHub\powerbi-powershell\refreshproduction.ps1:82 char:1
+ Invoke-RestMethod -Uri $uri –Headers $authHeader –Method GET –Verbose
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand

# This sample script calls the Power BI API to progammtically trigger a refresh for the dataset
# It then calls the Power BI API to progammatically to get the refresh history for that dataset
# For full documentation on the REST APIs, see:
# https://msdn.microsoft.com/en-us/library/mt203551.aspx 

# Instructions:
# 1. Install PowerShell (https://msdn.microsoft.com/en-us/powershell/scripting/setup/installing-windows-powershell) and the Azure PowerShell cmdlets (https://aka.ms/webpi-azps)
# 2. Set up a dataset for refresh in the Power BI service - make sure that the dataset can be 
# updated successfully
# 3. Fill in the parameters below
# 4. Run the PowerShell script

# Parameters - fill these in before running the script!
# =====================================================

# An easy way to get group and dataset ID is to go to dataset settings and click on the dataset
# that you'd like to refresh. Once you do, the URL in the address bar will show the group ID and 
# dataset ID, in the format: 
# app.powerbi.com/groups/{groupID}/settings/datasets/{datasetID} 

$groupID = "FIll Me In" # the ID of the group that hosts the dataset. Use "me" if this is your My Workspace
$datasetID = "FIll Me In" # the ID of the dataset that hosts the dataset

# AAD Client ID
# To get this, go to the following page and follow the steps to provision an app
# https://dev.powerbi.com/apps
# To get the sample to work, ensure that you have the following fields:
# App Type: Native app
# Redirect URL: urn:ietf:wg:oauth:2.0:oob
#  Level of access: all dataset APIs
$clientId = "FIll Me In" 

# End Parameters =======================================

# Calls the Active Directory Authentication Library (ADAL) to authenticate against AAD
function GetAuthToken
{
       $adal = "${env:ProgramFiles(x86)}\Microsoft SDKs\Azure\PowerShell\ServiceManagement\Azure\Services\Microsoft.IdentityModel.Clients.ActiveDirectory.dll"
 
       $adalforms = "${env:ProgramFiles(x86)}\Microsoft SDKs\Azure\PowerShell\ServiceManagement\Azure\Services\Microsoft.IdentityModel.Clients.ActiveDirectory.WindowsForms.dll"
 
       [System.Reflection.Assembly]::LoadFrom($adal) | Out-Null
 
       [System.Reflection.Assembly]::LoadFrom($adalforms) | Out-Null
 
       $redirectUri = "urn:ietf:wg:oauth:2.0:oob"
 
       $resourceAppIdURI = "https://analysis.windows.net/powerbi/api"
 
       $authority = "https://login.windows.net/common/oauth2/authorize";
 
       $authContext = New-Object "Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext" -ArgumentList $authority
 
       $authResult = $authContext.AcquireToken($resourceAppIdURI, $clientId, $redirectUri, "Auto")
 
       return $authResult
}

# Get the auth token from AAD
$token = GetAuthToken

# Building Rest API header with authorization token
$authHeader = @{
   'Content-Type'='application/json'
   'Authorization'=$token.CreateAuthorizationHeader()
}

# properly format groups path
$groupsPath = ""
if ($groupID -eq "me") {
    $groupsPath = "myorg"
} else {
    $groupsPath = "myorg/groups/$groupID"
}

# Refresh the dataset
$uri = "https://api.powerbi.com/v1.0/$groupsPath/datasets/$datasetID/refreshes"
Invoke-RestMethod -Uri $uri –Headers $authHeader –Method POST –Verbose

# Check the refresh history
$uri = "https://api.powerbi.com/v1.0/$groupsPath/datasets/$datasetID/refreshes"
Invoke-RestMethod -Uri $uri –Headers $authHeader –Method GET –Verbose

Line 78

Invoke-RestMethod -Uri $uri –Headers $authHeader –Method POST –Verbose

Appreciated if someone could help resolve this issue.

Thanks,

Anton