PayPal doesn't work

-- url of the page with the problem -- : la-dune-argentee.fr
-- HikaShop version -- : 2.3.4
-- Joomla version -- : 3
-- Error-message(debug-mod must be tuned on) -- : The operatoon can't succeed.

Hi

I have a problem with PayPal. When customers pay with PayPal after validating their informations, PayPal refreshes and says that the transaction can't succeed.
Need help please.
Regards

Hi,

What is the exact error message that PayPal gives to the customer ?