title: Coupons for In-app Billing
body: <p>We are about to release an application on the Android Market, with In-app Billing for subscription that unlocks certain features for a the subscription period.</p>
  
  <p>My boss now wants me to implement varying number of "<strong>free</strong> subscriptions" in the sense that:</p>
  
  <ol>
  <li>The "lucky user" downloads &amp; installs the application from the Android Market like any other customer (always free to install, but premium features require payment via In-app Billing).</li>
  <li>The "lucky user" receives some key via email that allows him or her to avoid going through the In-app Billing checkout process (i.e. actually pay). </li>
  <li>The key can only be used once.</li>
  <li>Entering the key via a menu item, enables subscription for X months, <strong>as if</strong> he actually paid via In-app Billing.</li>
  </ol>
  
  <p>The "key" basically acts like a coupon, but I haven't found any such option in the <a href="https://play.google.com/apps/publish" rel="noreferrer">Publisher's Console</a>.</p>
  
  <p>Do you know of any such feature or a simple way to implement the above without duplicating the customer database on our (the publishers) server?</p>