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 > Invites2. Click "Deactivate" to deactivate a particular invitation, or "Deactivate All" for all of them#MastoAdmin