title: PayPal Payments Standard custom HTML form; How does PayPal know who is submitting?
body: <p>I'm trying to get this form to initiate a donation using PayPal Payments Standard...</p>
  
  <pre><code>&lt;form action="https://www.paypal.com/cgi-bin/webscr" method="post"&gt;
    &lt;input type="hidden" name="cmd" value="_donations"&gt;
    &lt;input type="text" name="amount"&gt;&lt;/input&gt;
    &lt;input type="hidden" name="item_name" value="OrganizationXYZ Donation"&gt;
    &lt;input type="hidden" name="image_url" value="http://www.OrganizationXYZ.org/images/logo.gif"&gt;
    &lt;input type="image" name="submit" border="0"  src="https://www.paypal.com/en_US/i/btn/btn_buynow_LG.gif" alt="PayPal - The safer, easier way to pay online"&gt;  
  &lt;/form&gt;
  </code></pre>
  
  <p>This seems like it should work according to PayPal's <a href="https://cms.paypal.com/es/cgi-bin/?cmd=_render-content&amp;content_ID=developer/e_howto_html_formbasics">documentation</a>, but it doesn't. Instead I get this error: </p>
  
  <p><strong>"We cannot process this transaction because there is a problem with the PayPal email address supplied by the seller. Please contact the seller to resolve the problem. If this payment is for an eBay listing, you can contact the seller via the "Ask Seller a Question" link on the listing page. When you have the correct email address, payment can be made at www.paypal.com."</strong></p>
  
  <p>This error doesn't make any sense because you do not supply an email address in these forms. Yet it seems to me that my form needs to post <em>some</em> kind of identification- otherwise how would PayPal know which account is receiving the donation? Unless I register a domain vai my PayPal account settings, but there is no place to do that either.</p>
  
  <p>Does anybody have experience with setting this up?</p>