When I click the “add image” icon when composing a forum post, and then choose a video to insert from my iPhone, the error message is cut off. See attached screenshots.
Sorry, the forum is a third-party service we use and not under our control. I believe the error you are getting is the forum does not allow you to upload videos directly. You would first have to upload to something like YouTube and then you can paste the link in your forum post. This is a limitation of the forum service.