If you are seeing an Invalid or Amended Transactions, or Error #7 or #10002 at the top of your PRO Form, when checking out with Paypal, chances are you are using an API certificate rather than an API signature in your settings.
When integrating with Paypal, ensure that you are using API signature to successfully process and validate payments. Here’s a good tutorial to learn where to find the API signature:
https://developer.paypal.com/docs/classic/api/apiCredentials/#creating-an-api-signature