PayPal configuration
<p>I do PayPal integration, and I'm having two issues.</p>

<ol>
<li>In the settings of pay button you can specify a fixed price or drop-down list with a variety products and prices. How to make button (or URL address) for ufixed price? To be able select price before sending.</li>
<li>How to automatically receive notification of successful payment? Server must run the script, but only in case successful payment.</li>
</ol>