Every since the new PSN store got updated it's been wacky for adding funds.
You can also add funds from the SCE store and/or edit your billing info among other stuff. Here is the link.
Welcome to the forum.
Yes the store can sometimes be a little wonky with funds. It's happened to me to. The issue usually resolves itself in a day's time.
The above poster has also been helpful and check out that link.
I'm having the same problem it seems. I tried to add funds on the site but yesterday it kept telling me that it cannot accept it at this time and to come back later. Now when I try to do it, it says my credit card info is not valid and to please check my entries carefully. I've checked several times. The information is correct.
Adding on: I called sony up, seems it's my card company's problem. Will need to contact them.