dd wrt as a proxy client

I want to use a router in a network with a proxy. Without the router, everything works if you open the proxy settings in Windows and enter the address and port. No additional actions are required. I want the WiFi network users not to have to manually enter these parameters. The router has the following network interfaces:

br0       Link encap:Ethernet  HWaddr C8:B3:73:2B:B9:6C  
          inet addr:192.168.1.120  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
br0:0     Link encap:Ethernet  HWaddr C8:B3:73:2B:B9:6C  
          inet addr:169.254.255.1  Bcast:169.254.255.255  Mask:255.255.0.0
eth0      Link encap:Ethernet  HWaddr C8:B3:73:2B:B9:6C  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
eth1      Link encap:Ethernet  HWaddr C8:B3:73:2B:B9:6E  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
vlan1     Link encap:Ethernet  HWaddr C8:B3:73:2B:B9:6C  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
vlan2     Link encap:Ethernet  HWaddr C8:B3:73:2B:B9:6D  
          inet addr:10.134.4.122  Bcast:10.134.4.127  Mask:255.255.255.192
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

The router's IP address in the local network is 192.168.1.120. The router's IP address in the proxy network is 10.134.4.122. Proxy settings: IP 10.128.0.90 PORT 8080 In the router settings, I have recorded the following command in the startup:

#!/bin/sh
PROXY_IP=10.128.0.90
PROXY_PORT=8080
LAN_IP=nvram get lan_ipaddr
LAN_NET=$LAN_IP/nvram get lan_netmask

iptables -t nat -A PREROUTING -i vlan1 -s $LAN_NET -d $LAN_NET -p tcp --dport 80 -j ACCEPT
iptables -t nat -A PREROUTING -i vlan1 ! -s $PROXY_IP -p tcp --dport 80 -j DNAT --to $PROXY_IP:$PROXY_PORT
iptables -t nat -A PREROUTING -i vlan1 ! -s $PROXY_IP -p tcp --dport 443 -j DNAT --to $PROXY_IP:$PROXY_PORT
iptables -t nat -I POSTROUTING -o vlan1 -s $LAN_NET -d $PROXY_IP -p tcp -j SNAT --to $LAN_IP
iptables -I FORWARD -i vlan1 -o vlan1 -s $LAN_NET -d $PROXY_IP -p tcp --dport $PROXY_PORT -j ACCEPT

But the proxy is not working. What could be the problem?