What exactly do you mean by "bill payment"?
There are no bills to pay on 48 - you buy membership/add-ons as needed in advance.
You are not billed for them in arrears as you are on a bill-pay/fixed term contract mobile network.
What exactly are you trying to do - the exact steps that you take?
What happens?
Any error messages?
Are you using the app or the website?
If the former then try the latter as the app has been flakey for a while lately.
Are you sure that your card details are still valid?
Have you successfully used the same card for payments online/on 48 before?
When did it last work?
If you need to contact 48 support about this then see the links in my signature below.
