Google has increased the security for Gmail, and some customers might experience problems sending lessons with their Gmail accounts.
How to fix
This procedure is simpler and allows any application to log in using your Gmail username and password. Follow the instructions in the link then use your Gmail username and password when configuring email in Swing Catalyst.
Option 2 (more secure)
Step 1: Enable two step verification
Step 2: Generate App Password
Step 3: Copy and paste the generated password into the password field under Email Sharing in Swing Catalyst (make sure to click Save, then Test)
This solution is more secure as you will be generating a password specifically for email sharing with Gmail within Swing Catalyst. It requires you to first enable two step authentication. Follow the instructions in the link to create a separate app password for Swing
Example email from Google
The first time you try to use Swing Catalyst with your Gmail account you may receive an email like this. The link under "If this was you" takes you to option 1 above.