When logged into Google, take a look at what Google is telling you in that link that Google provides you in the error message. There are references to "2-Step Verification" for your account where you might need to enter an App password but I would say that it is MOST LIKELY, you will need to enable the "allow less secure apps" setting in your GMail account (described further down on that page).
Take a look here: Allowing less secure apps to access your account which is linked in that Google message. Clicking on the Allow less secure apps link is where you can TURN ON the "Access for less secure apps". Try selecting "Turn on" if you haven't got "Access for less secure apps" turned on and see if this helps you out.