Older versions of Windows 10 have issues with connecting to a L2TP or IPsec VPN connection. If you are unable to update your computer to the latest version 1909 or later, you may want to try this registry fix.
To add a necessary registry setting:
1. Press the Windows Key and R at the same time to bring up the Run box.
2. Type in: regedit and click OK. Click Yes if asked if you'd like to allow the app to make changes to your PC.
3. In the left pane, locate and click the folder: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PolicyAgent
4. Click the Edit menu and hover your cursor over New. Click DWORD Value. A new registry will appear in the right pane, named New Value #1.
5. Rename that file: AssumeUDPEncapsulationContextOnSendRule (this is case-sensitive and contains no spaces) and press ENTER.
6. Right-click AssumeUDPEncapsulationContextOnSendRule, then click Modify.
7. In the Value data box, type 2 and click OK.
8. Reboot the computer.
Try your connection again to see if this has resolved your issue. This fix will not fix all connection issues. Some connection issues may be caused by the wireless router or the Internet router. A reboot of your router may also resolve VPN connection issues.
We hope that this information is helpful. Please let us know how this has helped you or if you have additional questions. As always Firestone Technical Resources, Inc. is here to help with your computer support issues - "Providing personal service for your impersonal technology."