Apache ProxyPass websocket (wss) problem

<VirtualHost *:443> ServerName mysite.com ServerAlias www.mysite.com SSLEngine on SSLProxyEngine On ProxyRequests Off SSLCertificateFile /etc/apache2/ssl/mysite.com.crt SSLCertificateKeyFile /etc/apache2/ssl/mysite.com.key SSLCertificateChainFile /etc/apache2/ssl/ca.cer DocumentRoot /var/www/errorPages ErrorDocument 503 /503.html ProxyPass /503.html ! ProxyPass / http://localhost:3999/ ProxyPassReverse / http://localhost:3999/ RewriteEngine on RewriteCond %{HTTP:UPGRADE} ^WebSocket$ [NC] RewriteCond %{HTTP:CONNECTION} ^Upgrade$ [NC] RewriteRule .* ws://localhost:3999%{REQUEST_URI} [P] </VirtualHost>