Exdoc documentation could not be found

Looking at your mix.exs file you have:

docs: [
        main: "README", # The main page in the docs
        # logo: "path/to/logo.png",
        extras: ["README.md"]
      ],

For main: I believe it is expecting a module name, not a filename. So the index will be blank. That is perhaps why there is an error from Hexdocs. As far as the link you supplied above, it should be lowercase, and it works: https://hexdocs.pm/fat_ecto/0.1.3/readme.html