I cant recharge by icloud why ..tell me what ist do i have 20$ in my apple ID

 i have 20$ in my apple ID

You need to set your Apple Account balance as your default payment.

See -> Add a payment method to your Apple ID

Add a payment method to your Apple ID – Apple Support (UK)

See also -> What you can buy with your Apple Gift Card or Apple Account balance

What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)

and ⤵️

• You can't use your Apple Account balance to send gifts or gift cards.
• If you use Family Sharing, your family members can't spend your Apple Account balance. Funds that you add to your Apple Account balance are only available to you. Find out more about how purchases are billed to your Apple Account balance.
• Some purchases might require you to have a credit card on file, even if you use your Apple Account balance to make the purchase.

If you still need help, get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service