Okay, you have a fairly good understanding of current balance and statement balance. On a credit card there is a closing date , lets say the closing date is the 10th of the month , anything from the 11th of the prior month to the 10th of the current month are things you'd be billed for that's your statement balance it also includes interest from the prior month if you didnt pay that statement in full. The current balance are charges after the statement closing date, those are things you have not been billed for. The reason you cant make a payment online is because you havent been billed for anything yet. You only owe , when there is a statement balance.
I work in the credit card department at B of A