Error "500031" occurs when purchasing an application from App World using PayPal as a payment method

• BlackBerry® PlayBook™ tablet
• BlackBerry® smartphones
• BlackBerry App World™ for BlackBerry® PlayBook™
• BlackBerry App World™ for BlackBerry® smartphones
• DT 2985197

Regenerate payment pre-approval keys.  This can be done from the App World client on the BlackBerry PlayBook, the BlackBerry smartphone or from the BlackBerry Webstore.

 From App World on the PlayBook:

1. Open App World
2. Swipe down from the top bezel
3. Tap Payment Options
4. Tap PayPal
5. Tap Modify and enter PayPal email and password
6. Tap Authenticate

From App World on the BlackBerry Smartphone:

1. Open App World
2. Open My Account
3. Select Payment Option
4. Login using BlackBerry ID
5. Select PayPal
6. Select Next
7. When Prompted enter PayPal email and password
8. Select I Agree

From  the BlackBerry Webstore

1. In a web browser go to https://appworld.blackberry.com/webstore
2. Click Sign In (in the top right of the page)
3. Enter your BlackBerry ID username and password
4. Click Sign In
5. Once logged in click My Payment Options (in the top right)
6. Under Current Payment Option Selected click Modify
7. Click Pay with PayPal
8. Once redirected to the PayPal website, login using your existing PayPal account with the appropriate email and password
9. Click Approve

Note: using any of the above methods you should receive an email from paypal confirming you have signed up for pre-approved payments plan.

Try using a an alternate payment method. For example Credit Card or Carrier Billing (if available).