Round-robin between two VPNs with route tables and iptables

Question

I opened to vpn interfaces with

openvpn --config vpn1.ovpn
openvpn --config vpn2.ovpn

and I want to send all from my laptop by one of the vpns.

I prevented the vpns from changing my default gateway with pull-filter ignore redirect-gateway.

Now I need to distribute traffik between two vpn interfaces, tun0 and tun1.

The following code does not work:

#!/bin/sh /etc/rc.common
START=99

# Define your VPN server IP addresses and ports
VPN_SERVER1="146.70.116.194"
VPN_SERVER2="103.108.231.98"
VPN_PORT1=443
VPN_PORT2=443

start() {
    echo "Starting VPN Load Balancer..."

    # Flush existing rules
    echo "Flushing existing rules..."
    ip rule flush
    ip route flush table vpn0
    ip route flush table vpn1

    # Add default routes to the custom routing tables
    echo "Adding default routes..."
    ip route add default dev tun0 table vpn0
    ip route add default dev tun1 table vpn1

    # Add rules to select the appropriate routing table based on mark
    echo "Adding ip rule..."
    ip rule add fwmark 1 table vpn0
    ip rule add fwmark 2 table vpn1

    # Use iptables to mark packets and route them, excluding VPN server IPs and loopback traffic
    echo "Configuring iptables..."
    iptables -t mangle -F PREROUTING
    iptables -t mangle -A PREROUTING -i lo -j RETURN
    iptables -t mangle -A PREROUTING -d $VPN_SERVER1 -p tcp --dport $VPN_PORT1 -j RETURN
    iptables -t mangle -A PREROUTING -d $VPN_SERVER2 -p tcp --dport $VPN_PORT2 -j RETURN

    # Log new connections for debugging
    iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW -j LOG --log-prefix "NEW_CONN: "

    # Mark new connections randomly and ensure packets for existing connections stay consistent
    iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW -m statistic --mode random --probability 0.5 -j MARK --set-mark 1
    iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW -j MARK --set-mark 2

    # Save the mark for established connections
    iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW -j CONNMARK --save-mark
    iptables -t mangle -A PREROUTING -m conntrack --ctstate ESTABLISHED,RELATED -j CONNMARK --restore-mark

    # Ensure correct routing for the marked packets
    ip route flush cache

    echo "VPN Load Balancer started."
}

stop() {
    echo "Stopping VPN Load Balancer..."

    # Remove the rules and routes when stopping the script
    ip rule del fwmark 1 table vpn0
    ip rule del fwmark 2 table vpn1

    ip route del default dev tun0 table vpn0
    ip route del default dev tun1 table vpn1

    iptables -t mangle -F PREROUTING

    ip route flush cache

    echo "VPN Load Balancer stopped."
}

case "$1" in
    start)
        start
        ;;
    stop)
        stop
        ;;
    *)
        echo "Usage: $0 {start|stop}"
        exit 1
esac

Can you advice?