def METHOD_NAME(value: str) -> Optional["SigningPayload"]:
    try:
        value = json.loads(value)
        if not isinstance(value, list):
            raise ValueError("payload should be a list")
        username, email = value
        if not (isinstance(username, str) and isinstance(email, str)):
            raise ValueError("both username and email should be strings")
        return SigningPayload(username, email)
    except Exception:
        return None