OpenVPN client takes another network card IP address

[rodc]

Hello all,
I will try to explain my setup as brief as possible.
Basically I have a desktop computer connect to a Raspberry Pi, the latter being the OpenVPN server.

So:

RaspberryPi is connected to:
- WiFi network and the internet (192.168.1.20 255.255.255.0 | Gateway: 192.168.1.254)
- Ethernet cable directly to the Windows desktop (10.0.0.1 255.255.255.0)
- OpenVPN server running on 10.8.0.1

Windows desktop is connected to:
- WiFi network and the internet (192.168.1.10 255.255.255.0 | Gateway: 192.168.1.254)
- Ethernet cable directly to Raspberry Pi (10.0.0.2 255.255.255.0)

Everything is working fine. However, when I connect to the OpenVPN server on the Raspberry Pi through my smartphone, for example, and I get the IP address 10.8.0.2, if I ping the Windows PC the IP shown as source is actually the Raspberry Pi's network card (192.168.1.20) instead of the Ethernet card.
Is there anything I can do so when the VPN client access the Windows PC, it uses its own real IP? (in this case 10.8.0.2)?

I installed OpenVPN using this script: https://github.com/Nyr/openvpn-install/
In the setup process when it asks me my internal IPv4, I typed in the Ethernet's IP 10.0.0.1. I don't know if this makes any difference.

Thank you in advance

[TinCanTech]

Please see:
HOWTO: Request Help !