A layer is listed when it has a video fill, or when its name contains one of these words: video, vid, clip, footage, reel, placeholder. It also has to sit inside the frame you selected. Text layers never become video layers. Rename the layer or give it a video fill, then press the refresh arrow next to “Video layers”.
Try it on your own frame
Free to try, no account. Or watch the plugin work in the browser first.