If you're trying to update your iCloud Payment method and are having trouble, there are a few things you can check. First, make sure that the credit card you're using is valid and has been activated. You may also need to contact your bank or credit card issuer to verify that they allow online payments. Finally, make sure that you're signed in to the correct Apple ID when you try to update your payment method. If none of these solutions work, please contact Apple Support for more help.