If you're a Mastodon server admin, you can control whether or not your members can invite people to join. However, this setting is a bit hidden and not in an obvious place:
1. Go to Preferences > Administration > Roles > Default Permissions, tick or untick the box marked "Invite Users"
2. Click "Save Changes"
To cancel existing invitations:
1. Go to Preferences > Moderation > Invites
2. Click "Deactivate" to deactivate a particular invitation, or "Deactivate All" for all of them







