Cannot login to app on Mac OS - 'submit' button constantly greyed out

Have signed up for account, am logged into website, have downloaded app on Mac OS and attempting to login but I cannot because the submit button stays inactive even when email and password entered - this surely isn't a limitation of the free version? My standard use case is to add a computer so I can reach it from Windows work PC hence i have to log in on app so it knows of the PC when I log in at work