I can no longer download tickets from mail to wallet

I am getting nowhere in trying to sort out a problem that has only arisen recently.

Suddenly, I can no longer download a ticket from mail to Wallet. I get the message: 'This website is trying to show you a Wallet pass. Do you want to allow this?' When I press 'allow', nothing happens. What is going on? The ticket is for the Heathrow Express

[Re-Titled by Moderator]