Get a sandbox key (start here)

The front door. Pass an email and you get a real account with a key linked to it — that key can then create brands, run readiness checks, sync an agent to Google and mint itself a live key, with no dashboard and no password. Pass no email and the key can only simulate sends: fine for kicking the tyres, a dead end for anything else.

An email that already has an account is refused rather than served — otherwise anyone who knows your address could mint credentials inside your account.