[dmdsoftware]

I'm unable to use after successfully installing. It is displaying an invalid username/password or permission error

Did you use a prior version of the plugin?

I assume no. In that case, you may have 2 factor authentication or application passwords set on your account, which is perfectly fine -- I do as well. Log into Google on a web browser, and in under Account, select Security. There is an options "App passwords". Select settings and define an app and use that password in the plugin.