Adding a group to InviteMember is very similar to adding a channel.
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First, click Telegram Group:

You'll see a short video about how to create a new private group:

When creating your group, you should add the @InviteMemberBot as a member. You can check out our article about How To Create a Telegram Group.

When it's ready, hit Done.

After creating your Telegram Group you'll be asked to add the @InviteMemberBot to the group's administrators. It needs to have Invite Users via Link and Ban Users permissions:

Now that the @InviteMemberBot is an administrator with the proper permission, you'll be asked to make sure that the Remain Anonymous option is turned OFF. You'll see a short video explaining how:

Now you can post a message in the group and mention @InviteMemberBot. 

Next, go back to the @InviteMemberBot and you'll see a confirmation:

Done!

Note: When linking the resource as a discussion group for a public channel, enable the "only members" option in the channel settings. This will prevent people from joining without paying.