I am sorry to hear about the issues that you've experienced with the integration on your site. Please note that Sandbox is only a test environment, so what appears to be successful payments there may be a bit misleading. However, if you are concerned that your live environment integration is the issue, please feel free to submit a ticket with our Merchant Technical Support. They'd be happy to check things out. Just go to www.paypal.com/mts and click "Contact us" towards the bottom.
