@Sue-and-Peter0
You're probably referring to only one of your listings, since 2 of them do not have the "No extra charge".
Go into your Availability settings and insert a minor extra charge for a second person. From what I have gathered on various forums is that somehow some listings will not show the misleading 'no charge' if nothing is chosen upon setting up that listing. But once something has been chosen, it can't be reversed to show nothing. So the only way out is the extra-person charge.