First, go to your server.properties file and make sure enable-rcon is set to true, and keep a note of your rcon.password and rcon.port.
Then, Invite the bot to your Discord Server, and choose a channel where only people authorized to run rcon commands can view, then run /add_rcon:
You will get a modal, write your server ip, port and rcon password and click 'Submit'. You can verify by running /cmd list:
There are 7 players online.
If you recieve an error "Couldn't connect to server rcon", then make sure both port and password are correct and that you port-forwarded the rcon port. Otherwise contact support.