If one or multiple users never received their DUO 2FA invite email, and you've already confirmed it's not in their spam folder, resending the invite is quite simple.
1. Navigate to the Account > Integrations page and locate the DUO tile.
2. After clicking on the DUO tile, locate the user or users you'd like to have this recent to, and then click Resend Invite.
You can also call Support directly (305) 330-6677