I don't know what Dominos Ireland are up to with respect to their site. It's quite confusing and misleading.
If you go to the Irish site and login you get the below front page which clearly says that Paypal is available as a payment option. It's been like that for a couple of months:
But if you try to pay via Paypal you simply can't:
No explanation as to why they're advertising it and not actually taking it.