Create app-specific passwords for accounts with 2-step verification on:

Quick access: 

Go to https://myaccount.google.com/security

If you are on Google.com

Click on your icon on the top right

Click on Manage your Google Account

Click on Security

Scroll down further and Click on App passwords

Note: If app passwords is missing, that means your 2-step verification is off. You can turn on 2-step verificiation to see App passwords here. Or checkout the next section to allow less secure apps.

Make sure the right email is selected from the dropdown

Type password

Click on Next

Click on Other (Custom name) and name it SMTP integration (anything works)

Click on GENERATE

Drag to copy the highlighted text and paste it as the password when integrating Gmail SMTP

Now you can integrate within HighLevel in agency settings:

https://app.gohighlevel.com/settings/agency_smtp_service

Or go to the subaccount to integrate for the client:

Once you are in the subaccount

Click on Settings at the bottom left

Scroll further to Click on SMTP & Mailgun Services

Click on Add Service on the top right

Click on Select Provider

Click on Gmail

Paste the generated app password here and click Save, done!