iPlayTV supports VOD. You have to swipe right from your Apple TV remote to see other categories like VOD and all the channels. If you don't see that, then your provider doesn't have VOD. Again, iPlayTV on Apple TV 4 or 4K supports VOD.

I'd suggest you are using the wrong app.

VOD itself is already an uphill climb with IPTV providers, and even more so if you are targeting 4k content. I'd recommend you look into Kodi for that latter, and specifically use of the Gaia addon within it (gonna have to pay $4/mo for a real debrid account though, but that also completely negates any need to care about what VOD your chosen IPTV service might offer). Plenty of discussions on it found here: /r/Addons4Kodi/