Unable to install Norton Family on my son's Galaxy S7 -- certificate can't be validated

Hi I'm not able to add my son's Galaxy S7 to our Norton Family Premier account.  I installed the app to his phone, but when I go to sign in I get a pop up that says "Unable to sign in -- Certificate can't be validated on your device. Please make sure your device date is correct."  The date and time on the phone are correct. I've tried turning off the automatic network date and time but doesn't fix the problem.  Any suggestions?