Settings don’t work, and Critical error

Hi.

I just installed this plugin. It works correctly but I can’t see Settings tab, I got a blank page: https://prnt.sc/xng72h

And in Tools tab I got the critical error:
Fatal error: Uncaught Error: Call to a member function appendChild() on null in /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-content/plugins/wp-live-chat-support/includes/wplc_base_controller.php:86 Stack trace: #0 /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-content/plugins/wp-live-chat-support/modules/tools/tools_controller.php(15): BaseController->load_view(‘/var/www/vhosts…’, false, true, Array) #1 /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-content/plugins/wp-live-chat-support/includes/wplc_base_controller.php(39): ToolsController->view() #2 /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-includes/class-wp-hook.php(287): BaseController->{closure}(”) #3 /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(”, Array) #4 /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-includes/plugin.php(484): WP_Hook->do_action(Array) #5 /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-content/plugins/wp-live-chat-support/includes/w in /var/www/vhosts/xxxxxxxxxx/httpdocs/wp-content/plugins/wp-live-chat-support/includes/wplc_base_controller.php on line 86

Ha habido un error crítico en esta web. Por favor, comprueba la bandeja de entrada del correo electrónico del administrador de tu sitio para obtener instrucciones.

I have installed WordPress 5.6