I found the issue.
I have put a test environment in place over here: http://www.igerards.com/test
1. Please login there with the same login provided in the .txt
2. Then put this product in the cart: http://igerards.com/test/?product=test-product
3. Go to the cart (click the link under Done shopping? in the header)
4. Click proceed to checkout
5. You will find a box with this text: Have a coupon? Click here to enter your code
If you click 'click here to enter your code', a box should appear so you can enter a code. However, if Ajax Search Pro is activated, this ajax function will not work.
The conflict is between Ajax Search Pro and the plugin WooCommerce Advanced Ajax Layered Navigation.
Hoping you can check it out and make Ajax Search Pro work in harmony with the layered navigation plugin.