Hi. The folks from Peplink have given you the precise instructions you need to get going. I very much doubt there is a problem with the router.
The point is that the router and your PC normally have to be on the same subnet to communicate. So, change the IP address on your PC’s ethernet adapter to any other address in the 192.168.20. subnet except 192.168.20.1. Use a subnet mask of 255.255.255.0, as sitloongs suggested on July 11 of last year, and a gateway of 192.168.20.1, although the latter does not make any difference at this point. (These are pretty much standard instructions for configuring any router for the first time – not unique to Peplink.) I’m sure you know that after changing the settings on the adapter you normally have to deactivate and reactivate it (disable then enable in WIndoze).
It’s an excellent “box” – you’ll find it worth a few minutes to get it up, going and configured!