Option 1: Enable SMTP Authentication

Please help to turn off the second authentication. You can use google instructions as following: https://support.google.com/accounts/answer/1064203

Then, you can turn on the “allow less secure app access”. You can use this instruction as following: https://support.google.com/accounts/answer/6010255

Option 2: Don’t have to enable SMTP Authentication

In case the client does not want to turn off secondary authentication. Please find following steps to get app password.

1) You must have 2-Step-Verification enabled before setting up an application password. 2) Visit your App passwords page (https://myaccount.google.com/apppasswords). You may be asked to sign in to your Google Account. 3) At the bottom, click Select app and choose the app you’re using. You can also select Other and enter you own custom app name. 4) Click Select device and choose the device you’re using. You can also select Other and enter you own custom device name. 5) Click Generate. you can see the app password.