Webhook subscriptions not receiving all events

I set up a subscription of webhook for FireFly to send events to our app.
But our app have received a part of event's notice from FireFly.
I think that webhook subscription is permanence.
Is it right?

I send request body(below json) for "[POST] /api/v1/namespaces/default/subscriptions" to set up a subscription of webhook.
Did I get a wrong setting?

Now, after receiving event's notice, I set up a new a subscription of webhook to continuously receive event.

request body
```json
{
"options": {
"url": "http://:8082/emit",
"fastack": false,
"readAhead":100,
"method": "POST",
"withData": false,
"firstEvent": "oldest",
"headers" : {
"Authorization": ""
}
},

"namespace": "default",
"name": "emitSub",

"transport": "webhooks",
"filter": {
"topic": "string",
"events": "blockchain_event_received",
"blockchainevent": {
"message": {},
"transaction": {},
"listener": ""
}
}
}
```