Trying to fetch mail info using Microsoft Graph

# Replace these with your app registration details
$tenantId = "<YourTenantId>"
$clientSecret = "<YourClientSecret>"
$clientId = "<YourClientId>"

# OAuth 2.0 token endpoint for your tenant
$tokenUrl = "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token"

# Microsoft Graph API base URL
$graphApiUrl = "https://graph.microsoft.com/v1.0"

# The resource scope we are requesting (Mail.Read, MailboxSettings.Read, User.ReadBasic.All)
$scope = "https://graph.microsoft.com/.default"

# Request an OAuth 2.0 token from Azure AD using the client credentials flow
$tokenResponse = Invoke-RestMethod -Method Post -Uri $tokenUrl -ContentType "application/x-www-form-urlencoded" -Body @{
    client_id     = $clientId
    client_secret = $clientSecret
    scope         = $scope
    grant_type    = "client_credentials"
}

# Extract the access token from the response
$accessToken = $tokenResponse.access_token

# Headers for authenticated requests to Microsoft Graph
$headers = @{
    Authorization = "Bearer $accessToken"
}

# Function to fetch paginated results from Microsoft Graph API
function Get-PaginatedData {
    param (
        [Parameter(Mandatory = $true)]
        [string]$initialUrl
    )

    $results = @()
    $nextLink = $initialUrl

    while ($nextLink) {
        try {
            $response = Invoke-RestMethod -Uri $nextLink -Headers $headers
            Write-Host "API Response: $($response | ConvertTo-Json -Depth 3)" # Debugging the response
            $results += $response.value
            # Check if there is more data to fetch
            if ($response.'@odata.nextLink') {
                $nextLink = $response.'@odata.nextLink'
            } else {
                $nextLink = $null
            }
        } catch {
            Write-Host "Error fetching data from: $nextLink"
            Write-Host "Error Message: $_"
            break
        }
    }
    return $results
}

# Function to get all emails for a user
function Get-EmailsForUser {
    param (
        [Parameter(Mandatory = $true)]
        [string]$userPrincipalName
    )

    $mailApiUrl = "$graphApiUrl/users/$userPrincipalName/messages"
    return Get-PaginatedData -initialUrl $mailApiUrl
}

# Function to get attachment details for a specific email
function Get-AttachmentsForEmail {
    param (
        [Parameter(Mandatory = $true)]
        [string]$userPrincipalName,
        [Parameter(Mandatory = $true)]
        [string]$emailId
    )

    $attachmentApiUrl = "$graphApiUrl/users/$userPrincipalName/messages/$emailId/attachments"
    return Get-PaginatedData -initialUrl $attachmentApiUrl
}

# Function to get mailbox settings for a user (including last access time)
function Get-MailboxSettings {
    param (
        [Parameter(Mandatory = $true)]
        [string]$userPrincipalName
    )

    $mailboxSettingsApiUrl = "$graphApiUrl/users/$userPrincipalName/mailboxSettings"
    try {
        $mailboxSettings = Invoke-RestMethod -Uri $mailboxSettingsApiUrl -Headers $headers
        return $mailboxSettings
    } catch {
        Write-Host "Error fetching mailbox settings for $userPrincipalName"
        Write-Host "Error Message: $_"
        return $null
    }
}

# Step 1: Fetch only user mailboxes by filtering on userType eq 'Member'
$usersApiUrl = "$graphApiUrl/users?`$filter=userType eq 'Member'"
Write-Host "Fetching user mailboxes..."
$users = Get-PaginatedData -initialUrl $usersApiUrl

if ($users.Count -eq 0) {
    Write-Host "No user mailboxes found. Aborting script."
    exit
}

# Initialize result collection
$mailboxDataCollection = @()

# Step 2: Loop through each user and gather mailbox data
foreach ($user in $users) {
    $userPrincipalName = $user.userPrincipalName

    Write-Host "Processing mailbox for $userPrincipalName..."

    # Initialize user data
    $mailData = @{
        User                  = $userPrincipalName
        TotalEmails           = 0
        TotalAttachments      = 0
        AttachmentsTypeCount  = @{ 'PDF' = 0; 'Word' = 0; 'Excel' = 0; 'PPT' = 0; 'Image' = 0; 'Other' = 0 }
        LastEmailReceived     = $null
        LastAccessTime        = $null
    }

    # Get emails for this user
    $emails = Get-EmailsForUser -userPrincipalName $userPrincipalName
    foreach ($email in $emails) {
        $mailData.TotalEmails++

        # Track the last email received time
        if (-not $mailData.LastEm