Have you installed the stand-alone channel/app or are you trying to watch it through "The Roku Channel"?
https://channelstore.roku.com/details/6ce2b9d5a81cc1ee47b972259e534d87/curiositystream
I searched for CuriosityStream on my Roku box, not the Roku channel, then clicked on CuriosityStream. It brought up the channel with lots of shows on it, just like any other channel on my Roku box. I did not add the channel. I already have a CuriosityStream login, and I looked for a way to log into CuriosityStream on my Roku box, but did not find a way to do this without adding another subscription fee.
I only want to pay for the channel once, not twice. Maybe I'm missing a login somewhere on my Roku box?
First, I would click on that link I posted above. It's still not clear to me what version of Curiosity Stream you're using. If you already have the stand-alone channel it will state that when you try to add it from the link. If you don't then it will be added (overnight or the next time you restart your Roku or check for updates).
I have the standalone curiositystream channel app, there is a login scree but maybe not as obvious as it could be. Can't remember where at the moment (not at home to check) Keep looking
