At (2) and (3) note that a Developer Key is not the same as an access token. To get an access token with a Developer Key, you need to go through the OAuth process (see OAuth2 - Canvas LMS REST API Documentation).
(1) should give you a Manual Token (OAuth2 - Canvas LMS REST API Documentation), assuming your "new access auth" is the "New Access Token" button (at least that's what I see).
The manual token should work as you have tried. Maybe re-generate it and copy it carefully.
If that still does not work, perhaps post exactly how you are using it in your programming language. Easiest is if you can try a simple command-line example with curl. For example:
curl -k -X GET $server/api/v1/accounts/1/courses \
-H "Authorization: Bearer $token"