Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
Seems like Stremium is undergoing a certification testing process with Roku according to Stremium support to a Reddit user, but nothing is posted on the Stremium site, except under FAQS where mentions "Roku is in Development". https://www.stremium.com/faq/ Apparently they had to disable their beta while undergoing the certification process so currently no ability to use the present Channel or install new version until certification process is complete. Apparently, taking longer than the 24 hrs mentioned below as this was provided to a user 6 days ago. (However, just checked and their beta Channel is still available for install, just not the certified channel yet ). Not sure if it fully works as I don't use it. (no account)
"We're undergoing certification testing for the public Roku store so they said there could be 24 hours when our channel is transitioning where it's unavailable. We'll get it back online as soon as we're published."