Is it possible to connect a Deco P9 to an existing network via powerline only?

I have two Deco P9 units and would like to use them to extend my Wi-Fi to the basement. Unfortunately, there is no way that the Wi-Fi reaches down to the basement and I cannot pull any Ethernet cables either. My only option for connecting any unit in the basement to the main unit is via powerline.

The main unit is a Deco P9 in the living area. I am able to add the second P9 as a satellite to the network when it is inside Wi-Fi coverage on the same floor. However, I am unable to set up the same unit as a satellite in the basement. The setup process in the app fails when trying to connect to the Wi-Fi. I suspect the reason is that neither the Deco P9 nor my phone have a Wi-Fi connection to the main unit at any location in the basement.

The two P9 units are able to connect to each other via powerline, aren't they? How can I add the second P9 as a satellite without being in reach of the Wi-Fi network?

Thanks in advance