Your post was blank @Jamesd9938 and the subject line doesn't explain your issue or question clearly.
What exactly do you mean by "top up"?
Buying a membership plan, add-on or cash credit?
What happens when you try?
Any error messages?
When were you last able to successfully buy whatever you're trying to buy now?
What does your Transactions page say about recent payments?
If you need to contact 48 support about this then see the links in my signature below.
