AdobeSign API: Cannot create webhook (PERMISSION DENIED)

I have an application set up which has all OAuth scopes enabled with the modifier "Account" ("Self" was also tested).

The call is made as follows:

new WebhooksApi(apiClient).createWebhook(authorization, webhookInfo, null, null);

However, I always get the following error:

{
"code": "PERMISSION_DENIED",
"message": "The API caller does not have the permission to execute this operation"
}

Can anyone tell me what permissions are still needed? About the online swagger client I had the problem also already, mostly however it goes.