Has this ever happened to you?
More than half of the test subjects were confused by e-commerce checkout forms with an inline “Apply” button. The test subjects simply didn’t understand the concept of having a separate “Apply” button for distinct sections of a form – i.e. for applying a shipping method or a coupon code to the order. Instead, the subjects expected a single primary button in the checkout flows which would submit everything and take them to the next checkout step.
It has for me. Sometimes a final page in an purchase process has so many calls to action that I’m afraid to use them in case one of them makes the form start over. Ecommerce web site owners may find this article helpful.