Just to updated!
I managed to get Revolut App to authenticated BOI; via Safari website on a iPhone. I had to selected offload unused "BOI App" temporary on a iPhone to enable Revolut to allowed me to log in on the Safari URL/web address automatically not by BOI App.
Once authentically, it send you notification for the BOI App which you have to on-load use BOI App again and once sign in and confirm it, it goes into back to Revolut App successfully.
All sorted and I can now see my BOI current account linked and synced in Revolut.