Maybe try to restart both devices if you haven’t. I have ran into this issue multiple times before where it randomly just wouldn’t start but after a few minutes or to even a few days it would work as it should
Just did that too, didn’t work either. I also uninstalled and reinstalled Foreflight. That didn’t work either. Do the devices need to be the same? Like an iPad and iPad, or an iPhone and iPhone?
If you don’t have this option, you need to uninstall foreflight and reinstall it and then a pop up will appear when it tries to connect to the local network.