Codes are only valid for 5 minutes. If yours has expired you'll see "Code expired, please note that you have 5 minutes to verify the code before it expires"; if it doesn't match what was sent you'll see "Wrong code, please check the code that we sent to your email." Add ?regenerate to the verification page's URL (or simply revisit it after it auto-detects there's no active code) to have a brand-new code emailed to you, then enter that one instead.