Deterra is sold through AWS Marketplace. AWS sends you to this site to set up your subscription, and later to check on it. You always start from AWS Marketplace: this site has no login of its own.
Set up a new subscription
After you buy Deterra on AWS Marketplace, go to:
AWS Marketplace → Manage subscriptions → Deterra → Actions → Set up product → Set up your account
AWS then sends you to this site to register.
Check your subscription
Once you have registered, take the same route. AWS sends you to this site, which shows your subscription's status.