Hello to everyone.
I had the same problem like "This invoice has already been paid". Then it's just disapears. Don't know why, but now I don't see it.
But now I have another problem. I have my shop width PayPal Website Payments Standard width sandbox account. When I buy something, order is procedding alright, but after it I have no addition to my balance on sandbox. But funds withdrawn from the customer's account.
What is the problem?