pay for iCloud

Only by using Apple ID balance to prepay it; click here and see what options are available in your country. It'll be applied first whenever allowed, not just for the subscription.

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The billing is monthly, no matter what you do. As Niel mentions you can preload your AppleID balance with sufficient funds for a year, but the deductions for the subscription fee will still be applied and dedicated in monthly increments.

Apple removed all annual billing options years ago. There are only monthly subscriptions now.