Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
What site are you trying to buy credits from?
I presume you are trying to pay with a credit card or debit card. If so, try entering esp. your name and address data with the CAPS LOCK key in the On state, so that all letters are entered in ALL CAPS, like that.
Banking information, you see, is kept in upper-case letters, very often if not always. And some forms recognize the lower-case letters as an error because they are not an exact match to the information on record.
But let me know more about how you are trying to pay, and to what site, and I will instruct you as appropriate and as needed.