How to fix error error-ipsec-mm-auth-exists in Windows 11

Solution Steps

1. 1 Press Windows key + R, type "secpol.msc" and press Enter. This opens the Local Security Policy editor, where IPsec policies are managed.
2. 2 In the left pane, expand "Security Settings" and click on "IPsec Policies on Local Computer". You'll see a list of policies.
3. 3 Right-click on the policy that is causing the issue (or create a new one) and select "Properties". Go to the "Security Rules" tab.
4. 4 Look for any rule that uses the authentication method you're trying to add. If it exists, you can either edit the existing rule or remove it and re-add it. To remove, select the rule and click "Remove".
5. 5 If you need to add a new authentication method, click "Add" and follow the wizard. When you reach the "Authentication Methods" section, choose a method that is not already in use. If you get the error, go back and check the existing rules again.
6. 6 After making changes, click OK to save. Then, in the command prompt (Win+R, type "cmd", press Ctrl+Shift+Enter for admin), run "gpupdate /force" to apply the policy immediately.