Clear VPN Credentials
After updating your password, or encountering an authentication error, it is sometimes necessary to re-authenticate to the VPN.
The FortiClient Windows application often stores your credentials, and needs to have them manually cleared.
In the Windows search bar [Easily accessible by pressing the "Windows Key" on your keyboard],
type VPN Settings, then hit enter.
Once the Settings menu is open, click the down arrow next to the connect button for VPN.lyndendoor.com.
Next, click advanced options, then Clear sign-in info.
After you do that, try connecting again. It should ask for your credentials and then work.