Black screen on iPhone SE

Trying to “renew certificate” on my iPhone SE. Went through some login but now when I enter the Prey App I just get a black screen. What’s happened??
On my MBP everything seems to be working.

OK, I have deleted the phone from my MBP and deleted and re installed the App on my iPhone. Now everything seems to be working except that on the MBP in the Prey control page, when I open the iPhone I get the message that I need to “link to certificate”. Pressing that I get a message on the phone saying couldn’t connect, it says internet connection lost and on the MBP it says "accept the push on the device but I can’t work out how to do that.

However, now when I open Prey on the phone I get “Current status. Protected”. so I guess everything is OK apart from this certificate thing!±

Ensure a good internet connection or contact the app provider to fix the iPhone black screen issue or the certificate trouble.