can i pay iCloud storage by voucher

Not without supplying a credit card number; while iTunes Store credit can be used to pay for additional iCloud storage, Apple requires a credit card because it's a subscription model and not a one-time purchase.

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Not sure what you mean by vouchers, but here is what Apple says about paying for iCloud Storage:

Accepted payment methods for iCloud storage upgrades include credit cards, debit cards, and iTunes Store credit. If you don't have enough iTunes store credit to complete your upgrade, you'll be charged the remaining amount. Apple Store gift cards aren't accepted as payment for upgrading iCloud storage. Learn how to manage the amount of storage you're using

Cheers,

GB