Using Lightning AV Adapter

I connected my iPad to my TV with a new original Apple lightning AV adapter to watch a movie on Disney +. At first I could see content on the TV - my iPad desktop, then the D+ menu - but as soon as I clicked play on my selection, the TV screen either remained black or the D+ logo remained on the screen, but my selection didn't show up on the TV. I have a sound bar attached, sound came through that perfectly well. I disconnected and reconnected a few times, but it would always stop when I clicked to play my selection. Any ideas what I might be doing wrong? My TV is an LG, a few years old but otherwise in good order, my tablet is an iPad 5.