Enabling and disabling forwarding rule

Hello, 

We need to turn on a mail forwarding rule on a single mailbox, within 365. We looked at using a Azure Function App and copilot got us most of the way there but need some help with a 400 error.

Failed to enable rule: The remote server returned an error: (400) Bad Request.

The API authenticates and has the Mail.ReadWrite and Mail.Send and seems to be happy there. Is there a reason why this is giving a 400 error as all the details (I thought) were in order.

# Azure AD App details
$clientId = "your-client-id"
$clientSecret = "your-client-secret"
$tenantId = "your-tenant-id"

# Function parameters
$mailbox = "email address removed for privacy reasons"
$ruleId = "086b4cfe-b18a-4ca0-b8a6-c0cc13ab963e3208025663109857281"  # Provided rule ID without backslash

# Get OAuth token
$body = @{
    client_id = $clientId
    client_secret = $clientSecret
    scope = "https://graph.microsoft.com/.default"
    grant_type = "client_credentials"
}

try {
    $response = Invoke-RestMethod -Uri "https://login.microsoftonline.com/$tenantId/oauth2/v2.0/token" -Method Post -ContentType "application/x-www-form-urlencoded" -Body $body
    $token = $response.access_token
    Write-Output "Token acquired successfully."
} catch {
    Write-Error "Failed to get OAuth token: $_"
    return
}

# Enable the existing rule
$headers = @{
    Authorization = "Bearer $token"
    ContentType = "application/json"
}

$body = @{
    isEnabled = $true
}

try {
    $jsonBody = $body | ConvertTo-Json
    Write-Output "JSON Body: $jsonBody"
    $response = Invoke-RestMethod -Uri "https://graph.microsoft.com/v1.0/users/$mailbox/mailFolders/inbox/messageRules/$ruleId" -Method Patch -Headers $headers -Body $jsonBody
    Write-Output "Rule enabled successfully: $($response | ConvertTo-Json)"
} catch {
    Write-Error "Failed to enable rule: $_"
    Write-Output "Response Status Code: $($_.Exception.Response.StatusCode)"
    Write-Output "Response Status Description: $($_.Exception.Response.StatusDescription)"
    if ($_.Exception.Response -ne $null) {
        $responseContent = $_.Exception.Response.Content.ReadAsStringAsync().Result
        Write-Output "Response Content: $responseContent"
    } else {
        Write-Output "No response content available."
    }
}

# Return response
Write-Output "Script completed."