PlayStation store “We've encountered an error while processing your order” issue

This worked for me, try having caps on when you type in your billing address

did you log into ps store through PS4 or computer (browser)? there's a common issue about not being able to checkout via website no matter what payment type you try to use. on the other hand, if you log in directly through PS4, you can checkout no problem. i wasted a crap ton of time trying to get it to work on my computer, but gave up. just log in from the console now.

interestingly, if your purchase is $0 (eg monthly free psn plus games), you can checkout through website no problem.

if you're getting the error on the console, i have no suggestions.