Here is a forum thread on the Jellyfin forums from 2 days ago with an explanation and a solution. Looks like somehow the Roku Jellyfin client somehow has been marked as Beta which requires some extra steps for installation.

You could add Ombi to your software stack. It supports multiple push notification providers (WhatsApp is included I believe). Bonus is it will let your users add requests which can either be admin approved, or automatically added to your respective *arr downloader.