AzureFunction webhook does not return notifications

Question

Good day folks.

The issue I encounter is as follows:
I do not get any notification on any changes whatsoever.
Here's my Webhook:

public class NotificationHook
{
    private readonly AppSettings _settings;
    private IGraphClientService _graphClientService;
    private Subscription _subscription;

    public GraphNotificationHook(IOptions<AppSettings> options, IGraphClientService graphClientService)
    {
        this._settings = options.Value;
        this._graphClientService = graphClientService;
     }

    [FunctionName("Notification_Webhook")]
    public static async Task<IActionResult> SetupGraphHook(
    [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
    [DurableClient] IDurableOrchestrationClient client,
    ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

        var validationToken = req.Query["validationToken"];
        log.LogInformation($"Received Token: {validationToken}");

        // parse query parameter
        if (!string.IsNullOrEmpty(req.Query["validationToken"]))
        {
            log.LogInformation($"Received Token: {validationToken}");
            return new ContentResult { Content = validationToken, ContentType = "text/plain" };
        }
        using (StreamReader reader = new StreamReader(req.Body))
        {
            string content = await reader.ReadToEndAsync();      
            Notifications notifications = JsonConvert.DeserializeObject<Notifications>(content);

//exception thrown here as "notifications" is null
            /*
                if (!notifications.value.FirstOrDefault().ClientState.Equals("Test", StringComparison.OrdinalIgnoreCase))   
                    return new BadRequestResult();
            */

 //does not execute as notifications is null
            if (notifications != null)
                foreach (var notification in notifications.Items)
                    log.LogInformation($"Received notification: '{notification.Resource}', {notification.ResourceData?.Id}, {notification.SubscriptionId}");
        }
        return new OkResult();
    }
}

And here is how I create the subscription from inside the azure function:

[FunctionName("Start_Service")]
public static async Task<IActionResult> StarterService(
[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
[DurableClient] IDurableOrchestrationClient client,
ILogger log)
{
    await client.StartNewAsync("Create_Subscription");
    return new OkResult();
}

[FunctionName("Create_Subscription")]
public async Task<IActionResult> CreateSubscription(
[OrchestrationTrigger] IDurableOrchestrationContext context,
ILogger log)
{
    var subscription = new Subscription
    {
        ChangeType = "updated",
        NotificationUrl = $"{_settings.Ngrok}" + "/api/Notification_Webhook",
        Resource = $"groups/{_settings.Group_Id}" + "/members",
        ExpirationDateTime = DateTime.UtcNow.AddMinutes(15),
        ClientState = $"Test",
        //LatestSupportedTlsVersion = "v1_0"
    };

    var newSubscription = await context.CallActivityAsync<Subscription>("Authorize_Subscription", subscription);

    this._subscription = newSubscription;

    log.LogInformation($"Subscription added. Id: {newSubscription.Id}, Expiration: {newSubscription.ExpirationDateTime}");
    return new OkResult();
}

[FunctionName("Authorize_Subscription")]
public async Task<Subscription> CreateSubscriptionAuth(
[ActivityTrigger] Subscription subscription, ILogger log)
{
   return await _graphClientService.GetAppGraphClient()
        .Subscriptions
        .Request()
        .AddAsync(subscription);
}

Console Output:

Host lock lease acquired by instance ID '00000000000000000000000031BB71AF'.
Executing 'Notification_Webhook' (Reason='This function was programmatically called via the host APIs.', Id=82753e63-d6c6-475f-91c9-27d4776f5b4a)
C# HTTP trigger function processed a request.
Received Token:
Received Token:
Executed 'Notification_Webhook' (Succeeded, Id=82753e63-d6c6-475f-91c9-27d4776f5b4a, Duration=222ms)

Executing 'Start_Service' (Reason='This function was programmatically called via the host APIs.', Id=fbd63b1b-4dd4-4c26-8872-90975da80bf0)
Executed 'Start_Service' (Succeeded, Id=fbd63b1b-4dd4-4c26-8872-90975da80bf0, Duration=1355ms)
Executing 'Create_Subscription' (Reason='(null)', Id=7062303c-e04g-4d20-b50c-fa05ab5fb321)
Executed 'Create_Subscription' (Succeeded, Id=7062303c-e04g-4d20-b50c-fa05ab5fb321, Duration=304ms)
Executing 'Authorize_Subscription' (Reason='(null)', Id=859267fc-a011-4214-90c4-4d0fe3be18ea)
Executing 'Notification_Webhook' (Reason='This function was programmatically called via the host APIs.', Id=a4714942-a6ed-43cc-99fd-f9b0ea3f1e4b)
C# HTTP trigger function processed a request.
Received Token: Validation: Testing client application reachability for subscription Request-Id: 74da08aa2-d81e-4e97-92a8-c21051a1b1af
Received Token: Validation: Testing client application reachability for subscription Request-Id: 74da08aa2-d81e-4e97-92a8-c21051a1b1af
Executed 'Notification_Webhook' (Succeeded, Id=a4714942-a6ed-66cc-99fd-f9b0ea3f1e4b, Duration=43ms)
Executed 'Authorize_Subscription' (Succeeded, Id=859267fc-a011-4214-90c4-4d0fe3be18ea, Duration=6580ms)
Executing 'Create_Subscription' (Reason='(null)', Id=ccaf43b1-6909-48af-8bbd-b1c08b49f716)
Subscription added. Id: b8e73170-7d14-49df-acc2-fb6f7e21bd7c, Expiration: 2022-01-27 3:50:56 PM +00:00
Executed 'Create_Subscription' (Succeeded, Id=ccaf43b1-6909-48af-8bbd-b1c08b49f716, Duration=40ms)

But as stated above, no notifications appear whatsoever and the corresponding deserialized objects are null aswell as the request body being empty