The payment cannot be placed via
PayPal Standard Credit Card plug-in due to the error:
--->8--- [2013/08/28 17:04:12] [INFO]  [HSPC::MT::PP::PluginEngine::OP::__ANON__] process_task: process payment error=Internal error: 500 read failed: at /usr/lib/perl5/site_perl/5.8.8/HSPC/MT/Plugin/PP/OP_PayPalStandart/API.pm line 354 ---8<---
The URL for PayPal API URL (GetTransactionDetails API) (Signature authentication method) was incorrect:
Top > Commerce Director > Online Payments > Payment Plug-ins > <PayPal Standard Credit Card Plug-in> > PayPal Transaction Check API configuration
It should be "https://api-3t.sandbox.paypal.com/2.0/" instead of "https://api.sandbox.paypal.com/2.0/" according to developer's guide.
The problem has been fixed since version 4.3.4. Consider upgrading PBA-S to the most recent version.