Welcome to the Atlassian developer community @BozhidarCh,
I’m going to lock this thread because the discussion here hasn’t really clearly identified a problem, or a solution. My interpretation of your problem is the title of the topic, “OAuth token endpoint giving 404 error”. But I can’t really help with such little details. I can successfully run the authorization code flow, and the /oauth/token endpoint works correctly for me. All that explains is the service is not down for everyone.
It doesn’t help you. But to get an answer, we need a better question:
And, this community might not be the best place to get an answer because many steps in the OAuth flow have secrets. As such, the best place to get an answer about OAuth might be Atlassian developer support.