iPhone X and 11 Pro are perfectly compatible as long as the owner of the phones has NOT installed the iOS 14 beta. That version of iOS is what triggers the error because of changes Apple has made to iOS. The new Optik app that will be compatible with iOS 14 should be coming out around the time iOS 14 officially releases in the fall.
Also using Safari on an iPhone to access Optik will NOT work because Safari has never supported flash. Getting an error is the expected result.
I'm running the latest official release of iOS (13.6.1) on an 11 Pro and the Optik TV app works perfectly fine for me.
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