Edit payment info on icloud account

It would help a lot if you explained why you cannot edit it.

Here is how you update your payment method on an iPhone or iPad:

1. Open the Settings app.

2. Tap your name.

3. Tap Payment & Shipping (formerly Media & Purchases). You might be asked to sign in with your Apple ID.

4. Tap Add Payment Method, enter the new payment method, then tap Done.

5. Tap Edit.

6. Tap the red delete button next to the old payment method, then tap Delete.

For more information see this article about updating payment methods on various platforms (iPhone, Mac, etc.): If you need to change or update your Apple ID payment method - Apple Support

Also note: "If you change your address, the credit or debit card information that you use with your Apple ID might be automatically updated by your financial institution, and you don't need to take action. But if there's an issue [such as you having a subscription or being a Family Sharing Organizer], add a new card first, then remove the old card."

I have this same issue. What I've found is that it does not allow you to simply update the payment information, like the expiration date, if the only payment stored is the default payment. The only work around I've found is to add a new payment method temporarily and make it the default, delete the original default payment, then go back and re-add the original default payment with the correct details and you can then remove or keep the alternate payment method. I haven't figured out another way around it and can't find any articles that explain why this is the process.