Ask them to check the spam folder. If the invitation e-mail is not in this folder either or if the activation period of 48 hours has already elapsed, please go to the "Team" tab in the Account Portal. Search for the entry with your colleague's e-mail address and click on "Resend invitation e-mail" (this is the button with two arrows in a circle). An e-mail is then sent to your colleague again. If this does not work, please contact our helpdesk.