Can't create webhook through v2 api endpoint - smooch

Question

I am trying to dispatch webhook create endpoint and getting 403 Forbidden response code with no error information in body. My request looks like:
POST /v2/apps/618ce23498488b00e1582723/integrations/618ce235a6ccf400e1a4b992/webhooks HTTP/1.1
Host: api.smooch.io
Content-Type: application/json
Authorization: Bearer eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiIsImtpZCI6ImFwcF82MThjZTIzNGZiYTk5MDAwZTFiZDgyYWMifQ.eyJzY29wZSI6ImFwcCJ9.hXigeREGoUQ8YtM_gPUXfgWEGumbnlbBNLk_*******
Content-Length: 120
{
"target": "https://example.com/inbound-smooch-request",
"triggers": [
"conversation:message"
]
}
Response I am getting:
{"errors":[{"code":"forbidden","title":"Forbidden"}]}
That's how I generate Bearer token:
$signer = new Sha256();
$a = (new Builder())
->withHeader('alg', 'HS256')
->withHeader('typ', 'JWT')
->withHeader('kid', 'app_618ce234fba99000e1bd8***')
->withClaim('scope', 'app')
->getToken($signer, new Key('4K5KoVqLixLOUrkJSebr4rFsvZAu66d2WD8WEhXDgAZnJaltEpnHWpF_PUwQUGuNlFnBXvr8mtGsvNKj******'));
echo $a . PHP_EOL;
die();
Webhook api documentation: https://docs.smooch.io/rest/#operation/createWebhook
There is a bearerAuth (integration, app) explanation but there is no information what does this means. Documentation says that there are only two scopes: account and app. So what is this?
Other endpoints work normally (app create, app keys create, integration create)
Tried Basic auth also but it did not help.

Answer 1

The *Webhook endpoints are used (in v2) to create/update/remove webhooks from an existing customIntegration (integration with type: custom).
This endpoint will allow you to create a new integration, and when you set type: custom, it will also accept a webhooks list: https://docs.smooch.io/rest/#operation/createIntegration