I have a first generation Z Flip. It has been a while since I set up a camera and although I do recall having a little trouble, eventually it worked. Since the camera is set up now, it's a bit of a moot point.
My phone also works with the app, so I would suspect some other issue. Have you tried it with your phone connected to Wi-Fi as well as not connected? It should work both ways, but some people have had a problem when not connected to Wi-Fi. I haven't had to do it lately, but when the app first came out it seemed like I was constantly having to remove the app and reinstall it because I was getting errors.