Router - PiHole - VPN Settings

[suxus]

Hello
I'm looking for the right settings for router and Pihole.

I'm use a Asus RT-AC86U with Merlin 384.13
and a Raspberry with Pihole (IP: 192.168.98.75)

My current settings are

Router:
WAN section:
Connect to DNS Server automatically = YES

LAN section (DNS and WINS):
DNS Server 1 = IP-Address-PiHole (192.168.98.75)
DNS Server 2 = blank

Pihole:
DNS section
- Cloudflare DNS Server
- Listen only on interface eth0 (Checked)

That's all. Is this right?

My problem is, i setup a VPN connection (OpenVPN Client) to a NordVPN server and i set

Accept DNS Configuration = Exclusive
Force Internet traffic through tunnel = Policy Rules
Rules for routing client traffic through the tunnel
Source IP: IP-From-iPad
Destination IP: 0.0.0.0
Iface: VPN

So i want that the iPad use the VPN connection and use the DNS server from my VPN Provider (NordVPN), but when i make a check browserleaks.com/ip then i have the right IP, but the DNS server are from Cloudflare.

When i use the same ovpn-file from the router directly on my iPad with the OpenVPN App, then i have the right DNS server (no DNS server from Cloudflare).

I hope a expert see what's my problem.

Thank you very much.