With two-factor authentication, your account can only be accessed on devices you trust, like your smartphone or personal computer. When you want to sign in to your Bittrex account, you'll need to provide two pieces of information—your password and the six-digit verification code that's automatically displayed in your authentication app.
If you are having trouble with your two-factor authenticator, your device may not be syncing. The typical reason for two-factor failures is that the clock on your phone has drifted. We only have a two minute window for 2 FA confirmations so if your clock has drifted beyond that, you will not be able to login. Please make sure your phone is configured to sync your time with the cellular network.