I cannot sign in

Most sign-in problems are one of three things.

The password does not work

Use the "Forgot password" link on the sign-in page. The link that arrives is single-use and expires, so request a fresh one rather than reusing an old email.

If the link is missing, check whether the address you typed is the address the account was created with — a reset is never sent to an address with no account, and the page says the same thing either way on purpose, so that nobody can use it to find out who has an account here.

The verification email never arrived

Verification links expire. Sign in and request another from the banner at the top of the page.

The authenticator code is refused

Codes are tied to the clock on the device that generates them. If that clock has drifted, every code will be refused; enabling automatic time on the device fixes it. If the device is gone, use one of the recovery codes saved when two-factor was set up — each works once.