Why Fulfillment Service Callback Url Could Not Receive Message?

Question

[2023-04-05 10:51:13] local.DEBUG: FulfillmentServiceCreate Response: {"data":{"fulfillmentServiceCreate":{"fulfillmentService":{"id":"gid://shopify/FulfillmentService/64278757653?id=true","serviceName":"TSAS Fulfillment rajan1","callbackUrl":"https://5f12ed4af0ca.ngrok.app/api/fullfillment","fulfillmentOrdersOptIn":true,"inventoryManagement":false},"userErrors":[]}},"extensions":{"cost":{"requestedQueryCost":10,"actualQueryCost":10,"throttleStatus":{"maximumAvailable":1000,"currentlyAvailable":990,"restoreRate":50}}}}

successfully registered, but after placing order i am not able to receive any notification.

<callback_url>/fulfillment_order_notification.

$queryArr = [
            'query' => 'mutation fulfillmentServiceCreate($name: String!, $callbackUrl: URL!, $fulfillmentOrdersOptIn: Boolean!, $inventoryManagement: Boolean!) {
                    fulfillmentServiceCreate(name: $name, callbackUrl: $callbackUrl, fulfillmentOrdersOptIn: $fulfillmentOrdersOptIn, inventoryManagement: $inventoryManagement) {
                      fulfillmentService {
                        id
                        serviceName
                        callbackUrl
                        fulfillmentOrdersOptIn
                        inventoryManagement
                      }
                      userErrors {
                        field
                        message
                      }
                    }
                  }',
            'variables' => [
                    "name" => "TSAS Fulfillment rajan3",
                    "callbackUrl" => "https://9ff335e2924e.ngrok.app/api/fullfillment",
                    "fulfillmentOrdersOptIn" => true,
                    "inventoryManagement" => false,

            ]
        ];