Import certificate for win7 or older systems, fix ikev2 protocol 13801, authentication credentials not acceptable

As Microsoft has stopped updating and supporting Win7 and older systems, the built-in root certificate has expired, so you will need to import the root certificate manually to continue using it.

Download the root certificate file ISRG_ROOT_X1.cer, double click on it, click on "Import Certificate" and keep going through the next steps.