facetime
Why can’t I connect to FaceTime without the wifi
If you're trying to use FaceTime over cellular, make sure that Use Cellular Data is on for FaceTime. Go to Settings and tap Cellular or tap Mobile Data, then turn on FaceTime. If you're using an iPad, you might see Settings > Cellular Data.
For more info, see:
If you can't make a FaceTime call on your iPhone, iPad, or iPod touch - Apple Support