View Source Phoenix.NotAcceptableError exception (Phoenix v1.6.12)
Raised when one of the accept* headers is not accepted by the server.
This exception is commonly raised by Phoenix.Controller.accepts/2
which negotiates the media types the server is able to serve with
the contents the client is able to render.
If you are seeing this error, you should check if you are listing
the desired formats in your :accepts plug or if you are setting
the proper accept header in the client. The exception contains the
acceptable mime types in the accepts field.