Order created too early

[Quetzacoalt91]

The order is created too early in the payment process. You must call the function validateOrder(...) when the user has paid on your payment interface and comes back to PrestaShop, not before the redirection to your interface.

Currently, I meet the following issue when I select DotPay but finally want another payment module:
Cart cannot be loaded or an order has already been placed using this cart. I never tried to pay, but the order has been successfully created.