You are reading the documentation for the in-development version of Streamlink.
Like Crunchyroll, the FunimationNow plugin requires authenticating with a premium account to access some
--funimation-password. In addition, this plugin requires
incap_ses cookie to be sent with each HTTP request (see issue #2088). This unique session cookie
can be found in your browser and sent via the
$ streamlink --funimation-email='xxx' --funimation-password='xxx' --http-cookie 'incap_ses_xxx=xxxx=' https://funimation.com/shows/show/an-episode-link
There are multiple ways to retrieve the required cookie. For more information on browser cookies, please consult the following: