Critical error after activating the plugin

Hi, I installed and activated the free plugin and got the following error which I get warned about in a settings window:

“A critical error has occurred on your website. Check the site administrator’s mailbox for instructions.

Learn more about troubleshooting in WordPress.”

I received the error details on email:

Un errore di E_ERROR è stato causato nella linea 6520 del file /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/wp-mailinglist-plugin.php. Messaggio di errore: Uncaught TypeError: preg_split(): Argument #2 ($subject) must be of type string, array given in /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/wp-mailinglist-plugin.php:6520
Stack trace: 0 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/wp-mailinglist-plugin.php(6520): preg_split() 1 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/views/admin/metaboxes/settings-optin.php(26): wpMailPlugin->language_split() 2 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/wp-mailinglist-plugin.php(12849): include(‘…’) 3 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/helpers/metabox.php(288): wpMailPlugin->render() 4 /web/htdocs/www.pensierocritico.net/home/wp-admin/includes/template.php(1445): wpmlMetaboxHelper->settings_optin() 5 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/views/admin/settings.php(30): do_meta_boxes() 6 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/wp-mailinglist-plugin.php(12849): include(‘…’) 7 /web/htdocs/www.pensierocritico.net/home/wp-content/plugins/newsletters-lite/wp-mailinglist.php(9806): wpMailPlugin->render() 8 /web/htdocs/www.pensierocritico.net/home/wp-includes/class-wp-hook.php(308): wpMail->admin_config() 9 /web/htdocs/www.pensierocritico.net/home/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters() 10 /web/htdocs/www.pensierocritico.net/home/wp-includes/plugin.php(517): WP_Hook->do_action() 11 /web/htdocs/www.pensierocritico.net/home/wp-admin/admin.php(259): do_action() 12 {main}

thrown

How can I fix it? Thank you!

My current configuration:
WordPress version: 6.2.2
Php version: 8.0.27
Newsletters version: 4.9.2