My credit card expired on my iPhone. When trying to add the new credit card and selecting done, it doesn’t update. I’ve tried it several times with no luck. Any suggestions?

See the following Apple articles:

See this Apple article: Add money to your Apple ID balance

Add money to your Apple ID balance – Apple Support (UK)

Payment methods you can use with your Apple ID

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

If you can't make purchases or update apps, including free apps, you need to update your payment method or add a new one. 

Change, add or remove Apple ID payment methods

Change, add or remove Apple ID payment methods – Apple Support (UK)

Reasons your payment card may be declined

1.      Account suspended for suspected fraud.

2.      Address in your iTunes account does not match exactly the billing address for the card

3.      Error in credit card number

4.      Insufficient balance or you still owe money on a subscription

5.      The card was not issued in the country of the iTunes store

6.      Wrong expiration date

7.      Wrong security (CVV) code

8.     You are connected through a VPN provider that makes iTunes think you live elsewhere - uninstall VPN

Here is additional information from Apple if your payment method is declined.

If your payment method is declined in the App Store or iTunes Store - Apple Support