Once the option of 'Don't ask again on this device after verifying' is checked, it places a cookie on the specified device which is valid for 365 days and agency user won't be asked to enter the verification code again on the same device. If you are still asked to verify every time, please make sure your browser isn't set to clear cache and cookie upon exit.

On Chrome browser
  1. Select Vertical ellipsis button (User-added image) in the upper right corner 
  2. Select Settings > Privacy and Security
  3. Click Site settings 
  4. Scroll down to Additional content settings, click On-device site data
  5. Unselect Delete data sites have saved to your device when you close all windows
On Edge browser
  1. Select Horizontal ellipsis button (User-added imagein the upper right corner 
  2. Select Settings
  3. Select Privacy, search and services
  4. On Clear Browsing Data > click Choose what to clear every time you close the browser
  5. Toggle off Cookies and other site data 
  6. Close all Edge browser and reopen for changes to apply
On Safari browser
Safari doesn't have options to automatically clear cookies upon exiting.