title: How to check if email address entered in an input field exists in mailchimp list
body: <p>Wondering if anyone can help me. I am designing a wordpress website for a client and I need some help. I have installed Woocommerce 2.1.6 and was wondering how I would write a php script which, when the user goes onto a single-product page, instead of giving the default 'Add to cart' button, it shows a input field and a submit button. I would then like the php script to check if the email entered is in a mailchimp 'members list' that I have made.</p>
  
  <p>If it exists within the list, the add to cart button appears and can continue their purchase. If not, they are shown a message that they are not registered for a membership etc.</p>
  
  <p>Thanks everyone.</p>