case 1: when the password is wrong
case 2: when you try to login from a new App/domain/computer(This is the case in most scenarios when sending mail from code)
There is a solution for each
solution for case 1: Enter the correct password.
solution for case 2: generate an App Password for your SMTP codes
But what if you don't have access to the production server. try the below as well
You have to enable login from another timezone/IP for your google account.
To do this follow the link https://g.co/allowaccess and allow access by clicking the continue button.
And that's it. Here you go. Now you will be able to log in from any of the computers and by any means of the app to your google account.