API doesn't work

The API does not work. I've been trying for hours now. Neither the BCC mails create a request nor the API, although I have set everything up according to the API documentation, I always get an Unauthenticated. (HTTP status code: 401) error. What really surprises me is that after creating a campaign in the popup where I can select the automation, I am told to create an API key. I have done that and I have read the necessary permissions in the API documentation to create a request. So I selected the rights, saved the API key and continued with the setup in Zapier. The documentation no longer even mentions the generated API key. It exists, but does not need to be inserted anywhere according to the documentation. I find that strange. When I open the settings of the previously created API key, I can see the permissions again and none are ticked. If I select the desired rights again, click on save and open the settings again, all rights are deselected again.