On the onepage checkout page, I am able to go through everything: Billing Information --> Payment Information. Once I get to the Order Review and click on Submit, the page tries to submit the order (a good 5 second or more lag) then it takes me back to the checkout page. No sale is recorded.
Right now I am using the Braintree extension and Pay with Amazon extension. Still on RWD theme. This is a clean install with no modification except for the extensions.
Thanks for helping!
The domain name is otcshoppeexpress.com
Since the time I posted this, I have added a new theme. The result is still the same. When checking out, on (https://www.otcshoppeexpress.com/checkout/onepage/) I can complete all the steps up until it submits the order. Once it tries to place the order, it lags for at least 5 seconds (sometimes a bit more), and then it takes me back to https://www.otcshoppeexpress.com/checkout/cart/
Also I wanted to clarify that this is CE 220.127.116.11
Thanks for your help.
I see that when use Amazon payment method on your site we will meet the problem: 504 gateway timeout. I think you should increased the ELB timeout for requested ELB's.