Most likely this is because your devices are not set to internet time or are otherwise set to different time zones. Authenticators are time sensitive, so you will have to ensure that both your computer and your phone are displaying the same time correct to the millisecond. Within the time settings on your computer or phone there is a button such as “Set time and date automatically” or “Set time automatically”. Even if its enabled, try disabling and re-enabling it to be sure, this usually resolves any issues there are with your one-time-code being incorrect.