Critical Error on Office Extension

Hi, after I installed the extension I get this critical error on Post SMTP

An error of type E_ERROR was caused in line 74 of the file /home/marlowews/public_html/mavenpo.com/wp-content/plugins/post-smtp/Postman/Extensions/License/PostmanLicenseManager.php. Error message: Uncaught Error: Class name must be a valid object or a string in /home/marlowews/public_html/mavenpo.com/wp-content/plugins/post-smtp/Postman/Extensions/License/PostmanLicenseManager.php:74 Stack trace: #0 /home/marlowews/public_html/mavenpo.com/wp-content/plugins/post-smtp/Postman/Postman.php(193): PostmanLicenseManager->init() #1 /home/marlowews/public_html/mavenpo.com/wp-includes/class-wp-hook.php(287): Postman->on_plugins_loaded(”) #2 /home/marlowews/public_html/mavenpo.com/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array) #3 /home/marlowews/public_html/mavenpo.com/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #4 /home/marlowews/public_html/mavenpo.com/wp-settings.php(420): do_action(‘plugins_loaded’) #5 /home/marlowews/public_html/mavenpo.com/wp-config.php(106): require_once(‘/home/marlowews…’) #6 /home/marlowews/public_html/mavenpo.com/wp-load.php(37): require_once(‘/home/marlowews…’) #7 /home/marlowews/public_html/mavenpo.com/wp-admin/admin.php(34): require_once(‘/ho