I need to update my payment information

See -> If you need to change or update your Apple ID payment method

If you need to change or update your Apple ID payment method - Apple Support

See also -> Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

fyi: Not all credit & debit cards seem to work with App Store / iTunes Store, try a different one, or preferably a credit card. If your card is not accepted as a paymenf method, you need to contact your bank.

If you update your payment method or add funds to your Apple Account balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.

my information is up to date. I only have the one card. Why am I being asked to update my information or change cards? I checked, the funds are there for what I want.