Connection To Gmail Account From Another Application Not Working

Google has stopped supporting third-party apps:  

This means you will need to turn on MFA and create an app password in order to connect to your application.

The following guide walks you through the process: 

https://support.google.com/accounts/answer/185833?hl=en 

Create & Use App Passwords

If you use 2-Step-Verification and get a "password incorrect" error when you sign in, you can try to use an App Password.

1. Go to your Google Account.
2. Select Security.
3. Under "Signing in to Google," select App Passwords. You may need to sign in. If you don’t have this option, it might be because:
• 2-Step Verification is not set up for your account.
• 2-Step Verification is only set up for security keys.
• Your account is through work, school, or another organization.
• You turned on Advanced Protection.
4. At the bottom, choose Select app and choose the app you using Select device and choose the device you’re using Generate.
5. Follow the instructions to enter the App Password. The App Password is the 16-character code in the yellow bar on your device.
6. Tap Done.

Tip: Most of the time, you’ll only have to enter an App Password once per app or device, so don’t worry about memorizing it.