transactions fail in Membership Plugin

Using Membership plugin (not membership 2 yet). Recently, transaction keep coming back NULL, as displayed on the credit card screen. We recently changed hosts, but didn’t think that’s an issue. says that any solution using their PHP SDK needs to update. From their thread “If you are using our PHP SDK and have not updated since May 2015, you will likely need to update your cert.pem file.” I am wondering where this might apply or if it’s the likely reason that we have all transactions coming back displaying NULL onscreen. Thanks