Cathal What payment method were they trying to use? Credit/Debit cards? Do they use one of the support card networks (Mastercard/Visa)? In general, Irish cards are supposed to work, but we would need more information here to make better guesses at what the problem might've been.
As for the other payment methods, iDEAL is for people with Dutch bank accounts, Bancontact is for people with Belgian bank accounts, and SOFORT supports customers from Germany, Austria, Netherlands, Spain, Belgium, Italy. Therefore, if you're sending the link to people from Ireland the only option for them is using credit/debit card payment, if they're using an Irish bank.