(1) Check to see if they have confirmed your CrewMate invitation. If they have not received it then double check the email address for accuracy. We get lots of email bounce backs of CrewMates because the email was not entered correctly. Call your friend confirm exactly the email. Have them check their junk box and set up NauticEd as a safe sender.
(2) If your CrewMate is a NauticEd student then make sure that your email of your CrewMate is the same email address that they use to login. The email addresses must match.
(3) When you make multiple entires we don't send an email to your CrewMates each time. This would make them very mad. Instead we pile them up and send out one email each week max (none if there are none). In that email they can authenticate one at a time or "authenticate all".
(4) Your CrewMates do not need to be NauticEd students - but it is better if they are since they will get an automated logbook entry each time you make one when they were present on the boat. If they are a NauticEd student (take note of (2) above), they will be able to see the entry immediately when they login and will not have to wait for the weeks end as in (3) above.
Remember also that only one of you needs to make an entry. They other will automatically receive an authenticated log entry when they authenticate yours. Confer together while on the boat who will make the entry and on the details.