Some Paypal callbacks fail while others succeed

There are a number of reasons why some callbacks may fail; it could be a temporary network issue. But Paypal seems to be quite sensitive to non-western characters or other non-alphabetical characters in orders. This seems to affect the success of callbacks.

To address this, try the following:

1. Log into PayPal
2. Click the 'Profile' link in the menu bar under 'My Account'
3. Click the 'Language Encoding' link under the 'Selling Preferences' column
4. Click 'More Options'
5. Set 'Encoding' to 'UTF-8'
6. Set 'Do you want to use the same encoding for data sent from paypal to you?' to 'Yes'
7. Click 'Save'

UTF-8 is a larger character set, so using this setting should better handle orders with accented characters, ampersands and so on in the order.