question: ExpressVPN Keys does not prompt to save a login
answer: 
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  You will only be prompted to save a login via the ExpressVPN Keys Chrome extension when signing in or signing up for a new account on a website. This functionality is not currently available in ExpressVPN for Android or iOS.
  
  If it does not prompt you to save your login, you can report it as a bug by following these steps:
  
  Click the ExpressVPN Keys Chrome extension.
  Click the HELP tab.
  Click Report a problem.
  Follow the instructions.