Pi-hole does not manage your system's IP address, it just remembers it so it can display it on the dashboard and use it when blocking domains in an IP-based blocking mode.
That being said, you may have some luck with pihole -r.
Ensure you have a static or reserved IP established, either in your Pi configuration or by reserving the IP from the router. Note that IP and the interface, then run pihole -r and select "reconfigure". Then choose the IP and interface that you reserved.
From your debug log, the IPv4 address bound to the eth0 interface is:
192.168.13.4/24 does not match the IP found in /etc/pihole/setupVars.conf
OK, I ran the reconfigure and when I look at my pihole log file, nothing is going through. Could this be due to the fresh install of my piVPN? I believe that there is something that I need to change, but I can't find documentation on it.
Ok, I know that I'm missing something simple that I need to change in order to point the VPN to the pi-hole, but I'm not seeing where I need to change this.
I had just reinstalled piVPN and I didn't follow any other guide. I think there's something that I have to change again, but I can't recall what it is.