Hi,
1. No. The error messages are displayed by your template. Renaming the com_hikashop folder of your template removes the template overrides, but it doesn't change anything for the code displaying the error messages in your template :
www.hikashop.com/support/documentation/6...tibility-issues.html
2. It depends on the payment method. For most of them, you enter the credit card data on the payment gateway payment page and then the payment gateway notifies HikaShop of the payment. So the payment method cannot display the debug data directly and can only log it in a file so that you can review it later. For others, when the credit card data is entered during the checkout, the debug data can directly be displayed to you on the checkout so that it's either to debug the problem.