This issue can happen to customers at times but please don't worry. First thing we suggest to do is to check all details provided including expiry date and security code.
If the above doesn't work please call your bank and inform them of your purchase. They will tell you to wait 15 minutes and try again and the order should go through. The reason for this is usually because you are using a foreign card on an Irish website.
Some credit card issuers and banks require a prior notice from the card holder that the card will be used to purchase online. Please ensure your card issuer or bank is aware you intend to purchase online.