If you’re using PayPal as a gateway on your membership site, below is some information about a September 2015 update to require SHA-256 Compliance. This affects all sites using PayPal for Instant Payment Notification (IPN) on a non SHA-256 compliant server.
It is very likely that your hosting company or server has already been updated to support these new security requirements. However, if you are using an SSL certificate on your site (and especially if it was installed more than a few months ago), you may need to have your certificate reissued.
Read on for more details on how to test your SSL certificate and server and what to do.