The form we email a guest says they cannot board without it

A guest sent a participant form was asked to fill it in "before the trip — it only takes a minute", which reads as a courtesy. It is not: check-in refuses to let anyone board without their details, so a guest who treated it as optional found out at the dock.

The email now says what it costs — the same sentence the person booking sees when they choose to send a form rather than fill it in themselves.
Nothing else changed — the link, the form and the record of the send in Settings → Email activity are all as they were.