HDMI and IPhone XR problems

Hello, I’m having issues connecting my dads phone to the tv with a HDMI cable. We both have iPhone XR and it works for my phone and not his. It wont even show his home screen. Any suggestions on how to fix this? I have a Lightning Digital AV Adapter, and we have tried changing the iPhone cord and the HDMI cord and nothing is working. We have even tried different monitors.