Hello:
Anyone facing issues with getting registered on the site? I have tried both Visa and Mastercard and neither work.

Appreciate any feedback!

Mahesh

You want to buy a JR ticket online. The point of doing that is to get a reserved seat. The reserved seat ticket cost on the shinkansen is going to cost less than 900 yen. If you were to travel unreserved then you could just get the fare ticket at the station (you do want to get a reserved seat, tho(..What is the origin station of your trip (am asking this to find out which JR company)?

I have used eki-net to get reservations on JR East. JR-EAST Train Reservation | Top Page (eki-net.com)
If you try that and see a message that the site is undergoing maintenance or that you can't buy a ticket at this time then that means that you are outside of normal business hours in Japan. Try again after 7AM or 9AM Japan Time (they do show the hours on the website somewhere). The reason you need to do this is ..;. because Japan.

I googled and found that the smart ex issue is apparently a known thing. See the thread linked below. One of the replies mentioned using the full name on the account, not just the name on the card.
instead of Givenname Familyname, try
Givenname Middlename Familyname
Givenname M Familyname

Has anyone used Smart EX to book shinkansen? - japan-guide.com forum

Other names to try for any Japanese website, especially a J-language site:
Familyname Givenname
(i.e. try this even if the field labels on the form are "First Name" or whatever, Swap the order and put your lastname in the first name field, etc)

I have had to do the following on airline sites, like for name on passport, maybe elsewhere:
Givennamemiddlename Familyname (but all upper case)

I ran into this issue a few months ago too. As mrwunrfl says, make sure you try during daytime Japan hours. And you may need to record your name last name first name in katakana. Once I did both, it worked for me.

I only ever used English letters on a form, no katakana. Was on a hotel website.

I haven't encountered any issues with registration on the site, but it sounds frustrating that you're experiencing difficulties with both Visa and Mastercard. Have you tried reaching out to the site's customer support for assistance? They might be able to provide insight or resolve the issue for you.