Unable to purchase apps on App Store

Is there an error message? What happens when you try? Without knowing any details, the best I can do is suggest you contact iTunes Support. They can help.

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.

Copied from iTunes support - Apple Community

Billing error

Tomcat1800 wrote:

Billing error

iTunes Support can help with that. Please follow the instructions I provided.