New member having issues logging on

I’ve recently added a new member to our Trap NZ project. They’ve just got in touch to say they’re having to request a new login every time they’re adding a new record, every 2 to 3 days.
As I understand it, they’re using the link that Trap NZ initially emails to them when their email is assigned to a trap. Is this the best way to do it, or is there a simpler way?