Irish Rail

Did you warn your credit card issuer that you would be making purchases in Ireland BEFORE you tried to make the purchase?

Translink accepts PayPal, so if you have a PayPal account, that would be the easiest plan, or create one. In Ireland, online fares are significantly cheaper than tickets bought at the station (or through US agents).

I can't get to the window that asks for the credit card information. When I hit the button to order I get a window that shows my browser is working, San Jose Cloudfare (a security site) is working but Translink, host, is Error. I don't know why I get the error. I think this is a tech thing or this is a Nortern Ireland only site. Any suggestions?

I've often had trouble using my CapitalOne card to buy European rail tickets online while at home. It's pretty much as described in the OP - the transaction appears to be going well but it fails at final payment. Using a different card usually solves the problem, but then I have to remember to bring that card along (Deutsche Bahn says you need to have the payment card as proof of payer identity).

John, I would try a different web browser or see if your security settings allow adjustment. I had no problem getting to the payment page of Translink.co.uk yesterday using Internet Explorer. We do have a web security system here that we sometimes have to "click OK" to make web sites work, and I don't recall whether I had that issue.

I had similar problem using CapOne MC. I finally had to call the 800 number on the card and explain. After that the transaction went through. Internet purchase gives you a code that is input at the ticket machine at the station.
PS when you get the actual train ticket, it cannot be replaced if you loose it. You have to buy another one. So be sure to put it in a safe place. Lesson learned from sad experience.