Invoke-RestMethod - The remote server returned an error: (403) Forbidden

1. Created Service Principal account using the Azure App Register
2. Added API Permission, PBI Service and delegated Permission example as follows:

Report.ReadWrite.All or Report.Read.All

Dataset.ReadWrite.All or Dataset.Read.All

Below is my part of Powershell Script which call REST API to Export pdf file from Power BI Service report:

$authUrl = 'https://login.microsoftonline.com/tentid/oauth2/token';

$clientId="xxxxxxxxxxxxx"

$clientSecret = "xxxxxxxxxxxx"

$body = @{

    'grant_type' = 'client_credentials';

   'resource' = 'https://analysis.windows.net/powerbi/api';

    'client_id' = $clientId;

    'client_secret' = $clientSecret;

};

$authResponse = Invoke-RestMethod -Uri $authUrl –Method POST -Body $body

$authheaders = @{

    "Content-Type" = "application/json";

    "Authorization" = $authResponse.token_type + " " + $authResponse.access_token

    }

$groupid = "xxxxxxxxxxx"

$Reportid = "xxxxxxxxxxxxxxx"

$Body = "{`”format`”:`”pdf`”}"

$url1 = "https://api.powerbi.com/v1.0/myorg/groups/$groupid/reports/$Reportid/ExportTo"

$FileExport = Invoke-RestMethod -Method Post -uri $url1 -Headers $$authheaders -body $Body 

I get below error :

Invoke-RestMethod : The remote server returned an error: (403) Forbidden.
At C:\Users\eshahi\Desktop\101022.ps1:37 char:15
+ ... ileExport = Invoke-RestMethod -Method Post -uri $url1 -Headers $authh ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest)
[Invoke-RestMethod], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.I
nvokeRestMethodCommand