Creating webhooks: "The API caller does not have the permission to execute this operation"

[Gunther2514415098wp]

We have an application where users should be able to send documents to be signed via AdobeSign. In development I use Postman for example. I've had some problems with the Api (v6), but so far it works. What I can't get right though is creating WebHooks. My registered application actually has all the right (account), yet I get the following error: "The API caller does not have the permission to execute this operation". What else can this be due to?

Does the order in which the agreement is created matter?
Currently it is like this:

* Create TransientDocument
* Create Agreement as a draft.
* Transfer the signers
* Set Agreement to AUTHORING status
* Get signer
* Transfer FormFields
* Set Agreement IN_PROCESS

At which point do I create the webhook and how?