Dhcp server dont access internet

I have 2 ethernet cards in Ubuntu Server 20.04;

enp1s0 my main ethernet card,

enp2s0 my dhcp server ethernet card.

I want devices that receive ip via enp2s0 to access the internet, but if I set the enp1s0 interface to dhcp: false and define a static ip in netplan configuration, enp2s0 can access the internet. But when I do enp1s0 interface to dhcp:true, enp2s0 cannot access the internet. How can I fix this. Thanks for your help.

# /etc/dhcp/dhcpd.conf

default-lease-time 600;
max-lease-time 7200;
authoritative;

subnet 10.0.4.0 netmask 255.255.255.0 {
   authoritative;
   range 10.0.4.1 10.0.0.150;
   default-lease-time 3600;
   max-lease-time 3600;
   option subnet-mask 255.255.255.0;
   option broadcast-address 10.0.0.255;
   option routers 10.0.4.1;
   option domain-name-servers 8.8.8.8;
}

# /etc/netplan/xxx.yaml

network:
  ethernets:
    enp1s0:
      dhcp4: true
    enp2s0:
      addresses:
      - 10.0.4.1/24
      gateway4: 10.0.4.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]
  version: 2

# /etc/default/isc-dhcp-server

INTERFACESv4="enp2s0"

# /etc/sysctl.conf

net.ipv4.ip_forward=1
net.ipv4.conf.default.forwarding=1
net.ipv4.conf.all.forwarding=1

and my iptables rules;

iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
iptables -A OUTPUT -m conntrack --ctstate NEW,ESTABLISHED,RELATED -j ACCEPT
iptables -t nat -A POSTROUTING -o enp1s0 -j MASQUERADE
iptables -A FORWARD -i enp2s0 -j ACCEPT
iptables-save | sudo tee /etc/iptables.sav

after iptables rules;

sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"
iptables-restore < /etc/iptables.sav

my ip route command output;

default via 10.0.4.1 dev enp2s0 proto static 
default via 10.0.8.1 dev enp1s0 proto dhcp src 10.0.8.36 metric 100 
10.0.4.0/24 dev enp2s0 proto kernel scope link src 10.0.4.1 
10.0.8.0/24 dev enp1s0 proto kernel scope link src 10.0.8.36 
10.0.8.1 dev enp1s0 proto dhcp scope link src 10.0.8.36 metric 100