Many of us insert PayPal buttons into our posts and pages (see this tutorial for those instructions: https://www.blogsbyheather.com/2009/01/adding-a-paypal-button-to-a-post.html ). However, sometimes visitors who click those buttons "may" receive an error page. Therefore, add this piece of code to the first line of HTML code used to insert the PayPal button.
<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target=paypal>
This then forces the PayPal item for sale to be opened in a new internet/browser window and eliminates the possible error visitors may receive.