Get WhatsApp Business API up and running (using Postman)

I am trying to set up the WhatsApp business API client. I followed this instruction https://developers.facebook.com/docs/whatsapp/getting-started/#client-setup

At step 2 I installed "single instance" using this instruction https://developers.facebook.com/docs/whatsapp/installation/dev-single-instance

At Step 6 of the "single instance" instruction, I started Postman https://developers.facebook.com/docs/whatsapp/guides/postman.

At Step 4 of "Postman Collection" I configured AdminUsername (admin), AdminPassword (secret), NewAdminPassword (****) and URL (https://localhost:9090 [the example says 7901, but that results in error]). Response: some headers and "Status 401 Unauthorized".

Maybe this helps to find the cause: Following this post Whatsapp Business API production setup not working I ran this command docker-compose logs > debug_output.txt. This was the output: https://drive.google.com/file/d/1eXeaTeNiAiPW3A5bZ54gOg70UIPfF-vt/view?usp=sharing. (It doesn't make much sense to me...). I do have a MySQL WorkBench installed. No clue if it is installed in the same 'instance'.