Amazon Payments Don't Work

I setup Amazon checkout as a payment method in CS-Cart, but when I try to checkout using this method, I receive the following error. Any ideas how to fixe this

Hello knoxbury,

Please verify that the callback url was defined properly in your Amazon account.

Also please check if the HTTPS connection works properly on your server.

If the problem is still there, please contact us via Customer Help Desk and provide temporary FTP access to your server so that we could investigate the issue with your CS-Cart installation.

Anastasiya Kozlova

CS-Cart Support Team