title: PayPal Sandbox returns Invalid - IPN verification
body: <p>I need some help with PAYPAL IPN system . I am completely lost.</p>
  
  <p>I setup this form</p>
  
  <pre><code>&lt;form class="checkout-form" name="checkout-form" action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="POST"&gt;&lt;ul class="notices-box"&gt;&lt;/ul&gt;&lt;div class="row"&gt;&lt;div class="col-md-8"&gt;&lt;h2&gt;Order Details&lt;/h2&gt;&lt;div class="setting"&gt;&lt;div class="setting-label"&gt;&lt;/div&gt;&lt;input type="text" name="first_name" placeholder="First Name..."/&gt;&lt;/div&gt;&lt;div class="setting"&gt;&lt;div class="setting-label"&gt;&lt;/div&gt;&lt;input type="text" name="last_name" placeholder="Last Name..."/&gt;&lt;/div&gt;&lt;div class="setting"&gt;&lt;div class="setting-label"&gt;&lt;/div&gt;&lt;input type="text" name="user_address" placeholder="Address..."/&gt;&lt;/div&gt;&lt;div class="setting"&gt;&lt;div class="setting-label"&gt;&lt;/div&gt;&lt;input type="text" name="user_country" placeholder="Country..."/&gt;&lt;/div&gt;&lt;div class="setting"&gt;&lt;div class="setting-label"&gt;&lt;/div&gt;&lt;input type="text" name="user_telephone" placeholder="Telephone..."/&gt;&lt;/div&gt;&lt;div&gt;&lt;input type="hidden" name="action" value="checkout"/&gt;
  &lt;button name="submit" class="button-primary button-primary-for-checkout" style="width: auto; "&gt;Place Order&lt;/button&gt;
  &lt;/div&gt;&lt;/div&gt;&lt;!--end .part1.1--&gt;
  &lt;INPUT TYPE="hidden" name="cmd" value="_notify-validate"&gt;
  &lt;INPUT TYPE="hidden" NAME="return" value="http://zoomthe.me/paypalipn/paypal_ipn.php"&gt;&lt;INPUT TYPE="hidden" NAME="currency_code" value="USD"&gt;
  &lt;input type="hidden" name="amount" value="0"&gt;
  &lt;input type="hidden" name="email" value="zoomitflash-buyer-1@gmail.com"&gt;
  &lt;input type="hidden" name="business" value="zoomitflash-facilitator-1@gmail.com"&gt;
  &lt;input type="hidden" name="item_name" value="hat"&gt;
  &lt;input type="hidden" name="item_number" value="15"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>Here - <a href="http://zoomthe.me/soundportal//index.php?page=checkout" rel="nofollow">http://zoomthe.me/soundportal//index.php?page=checkout</a></p>
  
  <p>But when accesing the paypal site I get a big INVALID :(</p>
  
  <p>What should I do ?</p>