When I activate the PRO plugin I get the following error.
Fatal error: Can’t use function return value in write context in … \wp-content/plugins/sign-up-sheets-pro/controller/sheet.php on line 258
Contents of sheet.php line 258 below.
if (empty(Settings::isReceiptEnabled()) || !$signup || !$signup->isValid()) {
Just a quick update to this thread (since this was resolved directly via email)… the error mentioned above has been resolved and was related to running a PHP version earlier than 5.5.