There is a forum for PayPal questions: There are several recent topics that say that PayPal made a change that requires an updated certificate.  If you made no coding changes and it just stopped working, that seems the most likely explanation.  The up-to-date version is at If that is not it, it is barely possible that your host updated PHP in a way that broke your site.  But the certificate is both more likely and an easier fix, so I would check that before talking to your host.