Paypal problem: This invoice has already been paid

-- url of the page with the problem -- : private
-- HikaShop version -- : 2.3.2
-- Joomla version -- : 3.3.1
-- PHP version -- : 5.4.4

Hello,

I have a problem with paypal giving me the "This invoice has already been paid. For more information, please contact the merchant" error.

I have read your solution advice on www.hikashop.com/support/documentation/i...l-error.html#already

I have done the first part on paypal.com and also ALTER TABLE #_hikashop_order AUTO_INCREMENT=10000; But it it hasn't solved the issue.

At first it worked fine with sandbox. Then I changed to normal Paypal without sandbox and now back to sandbox which is giving me the error. (I have also deactivated some fileds in registration address information in the meantime)

When changing to normal Paypal the error says something like "Your payment can not be processed at the moment".

What could be the reason for this problem?

Thanks,
Andreas