To be added to the insider group we normally send you an invite by email when you join the Sweatflix membership. If you haven't received that email you can send me an email at firstname.lastname@example.org and I will have someone look into it.
I have received the email last week when I joined Sweatflix and clicked on "join the group" link and sent the request, but it seems that my request has been cancelled... :( I tried again today. Thank you for your help! :)