I just want to put some things out there for new people who haven't read through all the posts.

--IF YOU ARE USING NOSCRIPT on Firefox or another browser, DISABLE IT then try again.

--IF YOU ARE ABLE to purchase Crysta (meaning you don't get an error before you are able to choose an option), you have a couple choices, either buy it with Paypal with your credit card, Ultimate Pay using your credit card, or buying an Ultimate Pay Card either online or from local stores.
If you have errors using Ultimate Pay, give them a call at (650) 432-3200, and they'll be able to push Crysta to your account. ** Also, try using Hola Unblocker this time for your browser, then use Papal/Credit Card for crysta again

--IF YOU ARE UNABLE to get Crysta and your only option is to use a credit card then go to the Square Enix Account Management Page and try to update all your information, and update your credit card information there as well. Wait 24 hours and try again in Mogstation.

--IF YOU ARE IN EU and no other options have worked. There is a prepaid time card option for you for 60 days.

--OTHER SOLUTIONS
-Visa Electrons use Visa option, worked for some
-OUTSIDE of USA/CANADA but with NA billing address? Try using Hola Unblocker for Google Chrome