If you are seeing this error, it is likely due to not using your App Password when linking your Betterment account. Betterment has implemented an easy password generator to create app specific passwords that can be used to link accounts in specific applications. This means that you cannot use the normal login credentials to add your Betterment account: instead, you'll need to use your App Password. Please follow the steps below to generate the password on Betterment's website.
- Log in to Betterment and navigate to the Security tab under Account Settings
- Choose App Passwords
- Click Generate a New App Password
- When prompted to select application, choose "Personal Capital"
Once the password is generated, you will be shown the following disclaimer,
Lastly, we’ll show you the password we generated for you. We will only display this once. To use this password, simply copy and paste the 20-character password shown and use it to log in to the application you set it up for. You won't need to remember it, so don't write it down or share it with anyone.
Only connected applications can use this password to see your account. This password will not work for an advisor or other user trying to log in to your account from Betterment.com.
Please see this article for more information.