PRIVATE_GROUP_ID and PLUGIN_CHANNEL

Just create a new private group on telegram and make it a supergroup.

How to change a private group to supergroup?

Well it's damn easy. You just have to go the group settings and change Chat history for new members to Visible like below and save it.

Then add the rose bot (username is @missrose_bot)in the group and send a message /id. Just make sure that the replied value by the rose bot starts with -100... Then just copy it and use in setup.