How to fix error 809 when connecting to VPS via L2TP/Ipsec?

Question

VPN

Good day!
I rented a VPS with Windows Server 2019. I set up L2TP/IPSec VPN according to the instructions for the server . An attempt to connect according to the instructions for the device resulted in an error:
The logs say:

The SYSTEM user has established a remote VPN connection that has failed. Error code 809 returned.

What I did according to the advice of Google:

• Turned off the firewall (it was advised to open a number of ports, but I took the path of least resistance). I know that this cannot be done. I just had to make sure the firewall wasn't the problem.
  
• Disabled antivirus.
  
• Added entry AssumeUDPEncapsulationContextOnSendRule=2 (DWORD) to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PolicyAgent
  
• Added ProhibitIpSec=1 (DWORD) entry to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Rasman\Parameters
  
• Rebooted the device (and suddenly, and Google said after adding entries to the registry to do this).
  

Nothing helped, still the same 809 error. I ask for your help. Ready to provide any logs.
Thanks in advance!

Answer 1

Управление ALGyour router: enable L2TP ALGand IPSEC ALG.