First, please check that you have Flash installed on your device (https://get.adobe.com/flashplayer/).
Also, sometimes the videos will not work for certain web browser configurations (some plugins or extensions are incompatible). Trying with another web browser (Safari, Internet Explorer, Firefox, Chrome) usually works.
Also, FluentU relies on YouTube videos for content. So if you are in a place like mainland China where YouTube is blocked, then you will not be able to watch the videos on FluentU. We hope to offer a version that is usable for users without access to YouTube. But in the meantime, we highly recommend a quality VPN like 12VPN (https://getsetupfile).
For the foreseeable future, we will continue to rely primarily on YouTube because we haven't found another video platform with an API that is developer friendly enough.
There are a couple potential ways you can still use FluentU if you have an iPhone without YouTube
our audio dialogues don't require YouTube.
the review exercises in the app don't require YouTube either.