I've been stuck on this issue for literally hours just trying to find the answer to this.

I start with the Mac Terminal $ rails s and it loads puma & works fine until I run into the problem attached in the picture below.

CodePudding user response：

Are you running on a Ruby on Rails version that was released on the afternoon of 2021-12-14 – like 6.0.4.2, 6.1.4.2, and 7.0.0.rc2?

Then you should just update to the versions released later in the night because those versions had a bug in their default configuration

There was a bug in the default configuration of the previous release such that requests in development with a port number wouldn’t be considered “authorized” requests. Requests to “localhost:3000” should work in this new version.

Updating Ruby on Rails to any of these versions 6.0.4.3, 6.1.4.3, and 7.0.0.rc3 should fix the bug.