I tried to call someone on the duo. the person I was calling his video get stuck all the time but I can hear the voice clearly. The first time I think I am having issues with mobile data then I tried over wifi results are the same. but I can use other video calling apps like messenger and WhatsApp but I can't use duo for video call.

I have an iPhone, and I wanted to do the videocall but I have no idea which app is the best for video call, my friend recommended me the app facetime but I have no idea about how does FaceTime work on an iPhone?