Test Payment Gateway Account Fails
Cart66 only works with live payment gateway accounts except when using Stripe as your payment gateway. Cart66 will not work with test or sandbox accounts from other gateways because other gateways use different API end points for their test environments which are confusing to find and setup.
Cart66 Built-In Test Payment Gateway
To make testing your store easy, Cart66 comes with a built-in test gateway that you can use as much as you want for free when testing your store.
The one exception to this is Stripe (http://stripe.com) will work in test mode if you use your Test Secret Key in your Cart66 gateway configuration settings. Then when you go live, be sure to update your Cart66 gateway configuration to use your Stripe Live Secret Key to accept live credit card payments.