1) I requested the Device Type Identifiers from https://developer.amazon.com/frustration-free-setup/console/onboard/request-device-registration
2) About a week later, I received the email from FFS support team with DSS Public Key
3) I used the DSS Public Key to generate DAK and DHA keys and in the end I have obtained private_key.pem and certificate.pem from https://developer.amazon.com/frustration-free-setup/console/manage-daks?apid=ctw3
4) I replaced the keys with the newly generated pair and tried to connect Echo dot within 5 mins after setup.
5) Connection failed.
I had already send email to firstname.lastname@example.org but still not receive any response now.