You may see the following error when trying to invite participants to join your team:
You cannot invite this recipient. Please remove this e-mail.
In this case, the individual with that e-mail address has chosen to unsubscribe from all notifications from Big Team Challenge. Since this includes notifications inviting them to join your team, unfortunately we cannot create the invite and send out an automated email.
The best solution is to ask your friend / colleague to contact us directly from their email address via firstname.lastname@example.org, asking to be re-listed to receive notifications from Big Team Challenge.