Shopware 6 Wallee: Webhook Error (API Version not available)

Issue: 

Wallee Webhooks communication fails because of a reply saying HTTP 404 with this or a similar error in the response:

{"errors":[{"code":"0","status":"404","title":"Not Found","detail":"Requested api version v1 not available, available versions are v2, v3."}]}

Solution:

The Webhooks have to be updated. Shopware is using an API Version for all "URLs", which has to be updated in case shopware itself was updated.