Verify your email with the 6-digit code sent during sign-up.
On success, returns your API key:
New users: a freshly generated API key for your account.
Existing users: your existing API key is returned (use this to
recover a lost key).
The verification code expires after 24 hours. You have up to 10
attempts per code. If you exhaust all attempts, call sign-up again
to receive a new code.