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How signing in works
There is no password. Nothing to choose, nothing to remember, and nothing that can be reused somewhere else. You enter your email address and a sign-in code arrives in that mailbox.
Codes expire, and each one works once. If a code is rejected, request a new one rather than retyping the old one — an expired code and a mistyped code produce the same message.
Accounts are created by invitation only. Requesting a code for an address that has no account does nothing, and this page cannot tell you which case you are in — showing that difference would hand an anonymous visitor a list of valid accounts. If no code arrives, first check the spam folder, then check that the address is exactly the one the account was created with.