This wiki explains how to install and use HTTPs

Modify config.json to set isUseHTTPs:true:

• https://github.com/muaz-khan/RTCMultiConnection-Server/wiki/config.json

{
   "isUseHTTPs": true
}

Set valid certificate paths to sslKey and sslCert:

{
  "isUseHTTPs": "true",
  "sslKey": "/home/ssl/domain.key",
  "sslCert": "/home/ssl/domain.cert",
  "sslCabundle": ""
}

sslCabundle can be kept EMPTY. If you don't have .cabundle file then you must keep it empty.

sudo -s
apt-get install software-properties-common
add-apt-repository ppa:certbot/certbot
apt-get update
apt-get install python-certbot-apache
certbot --apache
certbot renew --dry-run

Ref: https://certbot.eff.org/lets-encrypt/ubuntutrusty-apache

Now config.json looks like this:

{
  "isUseHTTPs": "true",
  "sslKey": "/etc/letsencrypt/live/domain.com/privkey.pem",
  "sslCert": "/etc/letsencrypt/live/domain.com/fullchain.pem",
  "sslCabundle": ""
}

Do not remove any item from config.json. Only try to modify values. i.e. set true for isUseHTTPs etc.