If a user has not received the email with their invite to use a Final Draft 13 site license, please have the user check their spam folder. If it is also not in spam, please verify the exact email address to which the user should be receiving the invite.
It is also helpful to confirm if the user or the network they're using has a firewall, VPN, or other network environment which may require them to whitelist the "@finaldraft.com" email domain in order to receive emails from external senders.