WordPress Membership Plugin
Thanks for your quick reply admin. That fixed it. My hosting provider has changed the servers to provide current PHP so all is now working.
If it helps line 351 in class.swpm-auth.php is:
\Stripe\Stripe::setApiKey($secret_key);
correction: WP 4.8.1 was already installed. Just updated this plugin to version 3.5.6 from 3.5.5 and got syntax error.