1) Simply download the free LIVE Face app from the Mac App Store, and install onto your iPhone X. (Skip to Step #2 for second screen shot.)
2) Establish an intranet connection between the iPhone X and the computer, and make sure that they are on the same domain. You may connect to the same Wi-Fi network or use the iPhone X's hotspot to share a Wi-Fi internet.
More info:
http://manual.reallusion.com/Motion_LIVE_2D_Plugin/Resources/CTA_4/Plugins/Motion_Live_2D/UI_Intro_for_LIVE_FACE.htm
3) For smooth frame rate without lag, use a USB Connection: -
http://manual.reallusion.com/Motion_LIVE_2D_Plugin/Resources/CTA_4/Plugins/Motion_Live_2D/Connecting_to_LIVE_Face.htm
Please take note that only LIVE FACE(iPhone) v1.0.5, or higher version is compatible with Cartoon Animator 4.