10525 error with Paypal Express Checkout

-- HikaShop version -- : 2.3.2
-- Joomla version -- : 3.3.3
-- PHP version -- : 5.4
-- Browser(s) name and version -- : chrome
-- Error-message(debug-mod must be tuned on) -- : Connection failure - error code : 10525 , error message : This transaction cannot be processed. The amount to be charged is zero.

I'm using paypal express checkout as my only payment method. After clicking the "checkout with paypal" button I get this error message :
Connection failure - error code : 10525 , error message : This transaction cannot be processed. The amount to be charged is zero.

What has gone wrong?

Hi, to demonstrate the problem, I've installed hikashop starter to this live website:

www.peaceevercelebrity.tv/index.php/cart

Please take a look. I can give you access to back-end if needed.

I have only one paypal account. I'll erase paypal API Infos before I give the bank-end to you. I hope thats OK.

Email sent via contact form, please check.

Please be noted that the hikoshop page doesn't have a explicit menu item, please use www.peaceevercelebrity.tv/index.php/cart to check the page.

Thanks. I input correct API info, it seems to be working now.
But since this is just a test site, I need to fix this issue on my actual site. So could you please teach me how to fix that issue?