Why does it say unable to complete purchase when I added 10$ to my account

Raicya wrote:

you need• to set your Apple Account balance as your default payment.

No need to set it, it is always tried first.

How apps, content, and subscriptions from Apple are billed - Apple Support

"When you buy items or pay for subscriptions, Apple attempts to charge your payment methods in this order:

1. Apple attempts to use your Apple Account balance to cover the full amount.
2. If you don't have Apple Account balance or you don't have enough to cover the full amount, Apple attempts to charge your primary payment method. The primary payment method is at the top of the list in Settings on your iPhone. You can control which payment method is at the top of the list.
3. If there's a problem with the primary payment method, or if the primary payment method can't be charged for the full remaining amount, Apple attempts to charge your other payment methods in order from top to bottom. If none of them can be charged, Apple might try again."

it saying unable to complete purchase

Do you see a "Your purchase could not be completed" message?

A likely reason for seeing this message is Apple cannot find a functioning payment method to use in making this purchase. You may not have the kind required or there may be problems with the ones you do have.

Use the document Add a payment method to your Apple ID - Apple Support to review your payment methods such as credit or debit cards. Problem methods will usually have a notice in red lettering below them. The article If your payment method is declined in the App Store or iTunes Store - Apple Support has some information about declined payment methods.

If using Apple Account balance to pay for an item, ensure there is adequate balance to pay for the item, including tax if applicable. Read this article about how to check your Apple ID balance.--> Check your Apple Account balance - Apple Support Some purchases may require the presence of another payment method such as a credit card even if the final payment will be made by account balance.

Providing a comprehensive listing of all possible issues and their solutions would be excessive in a single reply. If the information above does not indicate the nature of the problem then you may find the fastest route to resolution would be to accept the invitation to contact Apple for assistance with this.

To contact iTunes Support, do this:

1. Click on this link --> Choose your country or region - Official Apple Support

2. Select your country

3. Select: Billing & Subscriptions

4. Select: Subscriptions & Purchases

5. Select: Update payment method

6. Select a chat session or a phone call.

If you update your payment method or add funds to your Apple Account balance, It would take about 1 to 3 business days in order to process.

If you're still unable to update your payment method, Contact Apple Support.

Then see -> Add a payment method to your Apple ID -> Add a payment method to your Apple ID – Apple Support (UK)

• if you use your Apple Account balance, you need to set your Apple Account balance as your default payment.

If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK)