wepay/PHP-SDK — pull request #5 by vrana (2013-05-19 05:47:16+00:00)
Title: Specify $arg_separator in http_build_query()

It defaults to arg_separator.output which may not be understood by WePay servers.

This parameter is available since PHP 5.1.2, I'm not sure what's the minimum PHP version supported by the SDK.