Creating permissions report on Devops

[5H4F33]

Hello everybody,

I'm trying to create a permission report on devops using rest api. I'm following the below doc:

https://docs.microsoft.com/en-us/rest/api/azure/devops/permissionsreport/permissions

report/create?view=azure-devops-rest-6.0

Below is the code I currently have:

# Create needed variables
$OrganizationName = "myorg"
$AdminUser = "myemail@domain.com"
$Token = "pattoken"

# The Header is created with the given information.
$base64AuthInfo = [Convert]::ToBase64String([Text.Encoding]::ASCII.GetBytes(("{0}:{1}" -f $AdminUser, $Token)))
$Header = @{
    Authorization = ("Basic {0}" -f $base64AuthInfo)
}

# Splat the parameters in a hashtable for readability
$Uri    = "[URL unfurl="true"]https://dev.azure.com/$OrganizationName/_apis/permissionsreport?api-version=6.0-preview.1"[/URL]

$Body = @{
    descriptors =   ""
    reportName  =   "testreport"
    resources   =   "collection"
}
# Store response
$Reports = (Invoke-RestMethod -Uri $Uri -Headers $Header -Method POST -Body $Body)
$Reports

Im getting below error:

Invoke-RestMethod : {"$id":"1","innerException":null,"message":"The request indicated a Content-Type of \"application/x-[URL unfurl="true"]www-form-urlencoded\"[/URL] for method      
type \"POST\" which is not supported. Valid content types for this method are: application/json,
application/json-patch+json.","typeName":"Microsoft.VisualStudio.Services.WebApi.VssRequestContentTypeNotSupportedException,
Microsoft.VisualStudio.Services.WebApi","typeKey":"VssRequestContentTypeNotSupportedException","errorCode":0,"eventId":3000}
At C:\Data\az_permissions.ps1:21 char:13
+ $Reports = (Invoke-RestMethod -Uri $Uri -Headers $Header -Method POST ...
+             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
    + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand

Im not sure how to move forward. I'd appreciate any help.

Thanks & regards.