which will do already the authorizations internally
Configuring the external Application will be done as described within the already shared link:
From the screenshots above we would recommend, once the overall-goal is cleared to focus on details like Application type (e.g defines the Grant Type), right scope settings…
From your screenshot above we can derive, that at least the URL looks not convincing. Also have a look here:
If no, endpoint url you are using to generate yoke is not correct. And also the parameters you are using are incorrect. You also need to use scope.
Please refer below post for what parameters to use and endpoint. This will help you generate access token which can then be used in next step to post queue items.
Please note that your scopes can not be all 3 scopes.. or.queues or.queues.read or.queues.write