If you're trying to remove your payment method because you don't recognize a charge, see why you were charged.
See if you have a subscription
To see your subscriptions on your iPhone or iPad, go to Settings, tap your name, then tap Subscriptions. If you have any active subscriptions, including iCloud+, you must have a payment method on file.
*Before you cancel your iCloud+ plan, use a Mac or PC to back up your devices.
Turn off purchase sharing
If you're in a Family Sharing group and you use purchase sharing, the family organizer must have a payment method on file. If you're the family organizer, turn off purchase sharing, then try to remove the payment method again.
Pay an unpaid balance
After the balance is paid, you can remove your payment method.
Get more help
If you still can't remove a payment method, contact Apple Support.