'Your Purchase Could Not Be Completed' error on the App Store

If you are showing this to us and mean to ask what you should do, then the answer is to do as your screen shot suggested. Contact iTunes support for assistance. Perhaps the instructions below will 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