title: Select amount with Paypal donation button
body: <p>I try to create donate via PayPal button and add custom select with amount.
  I tried to add something like this:</p>
  
  <pre><code>&lt;label for="amount"&gt;Select the amount you wish to donate:&lt;/label&gt;
  &lt;input type="hidden" name="currency_code" value="EUR" /&gt;
  &lt;select id="amount" name="amount"&gt;
    &lt;option value="25.00"&gt;€25.00&lt;/option&gt;
    &lt;option value="35.00"&gt;€35.00&lt;/option&gt;
    &lt;option value="50.00"&gt;€50.00&lt;/option&gt;
    &lt;option value="75.00"&gt;€75.00&lt;/option&gt;
    &lt;option value="100.00"&gt;€100.00&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>but PayPal simply doesn't recieve selected value.
  What I'm missing?
  What custom variables should I put into button generator form?</p>