In app purchases

If you get a message -> Your purchase could not be completed, you need to update your payment method or add a new one. 

• If you want to change your card, add first the new card, then remove the old one.
• or if you use your Apple ID balance, you need to set your Apple ID balance as your default payment.

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

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

If you update your payment method or add funds to your Apple ID 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.

Click here for more support and assistance.

We’d like to help but need more information such as - which app? Which games? Is there an error message?

You may find this helpful in letting us know exactly what the problem is:

Writing an effective Apple Support Commun… - Apple Community