BE9300/Flint3 IOT VLAN configuration For wired LAN3/4, Fiber configuration ok but no internet access

I made a factory reset and configured the access as per ISP params, everything’s ok, both wired and wireless connections do have internet access.

Then I logged in via SSH to create a VLAN for IoT as per this howto, committed & rebooted.
And again, internet working as a charm, VLAN created for IoT (only wireless devices).

So, apparently the script I made to add the vlan for surveillance devices is the culprit.
I made this lurking some scripts here in the forum and adjusting what I thought to be a correct change… but it seems I introduced something that broke the WAN.

Would anyone of you experts be so kind to help me figuring whar’s wrong?
Here’s the desiderata: a VLAN (192.168.50.x) for LAN3 and LAN4. I will connect an antitheft system to LAN3 and a NVR POE to LAN4. Specifically for the antitheft system, I will also have to open some ports to allow remote maintenance by the technician… but that’s another story.

My script:

* Surveillance/Security VLAN *

uci set network.vlan_surv='switch_vlan'
uci set network.vlan_surv.device='switch1'
uci set network.vlan_surv.vlan='50'
uci set network.vlan_surv.ports='3t 4ut 5ut'

uci set network.eth1_50=device
uci set network.eth1_50.type='8021q'
uci set network.eth1_50.ifname='eth1'
uci set network.eth1_50.vid='50'
uci set network.eth1_50.name='eth1.50'

uci add network device
uci set network.@device[-1].type='bridge'
uci set network.@device[-1].name='br-surv'
uci add_list network.@device[-1].ports='eth1.50'

uci set network.surv=interface
uci set network.surv.proto='static'
uci set network.surv.device='br-surv'
uci set network.surv.ipaddr='192.168.50.1'
uci set network.surv.netmask='255.255.255.0'

uci set dhcp.surv=dhcp
uci set dhcp.surv.interface='surv'
uci set dhcp.surv.start='100'
uci set dhcp.surv.limit='150'
uci set dhcp.surv.leasetime='12h'

uci add firewall zone
uci set firewall.@zone[-1].name='surv'
uci set firewall.@zone[-1].input='ACCEPT'
uci set firewall.@zone[-1].output='ACCEPT'
uci set firewall.@zone[-1].forward='REJECT'
uci add_list firewall.@zone[-1].network='surv'

uci add firewall forwarding
uci set firewall.@forwarding[-1].src='surv'
uci set firewall.@forwarding[-1].dest='wan'

uci add firewall rule
uci set firewall.@rule[-1].name='Allow-DHCP-Surv'
uci add_list firewall.@rule[-1].proto='udp'
uci set firewall.@rule[-1].src='surv'
uci set firewall.@rule[-1].dest_port='67-68'
uci set firewall.@rule[-1].target='ACCEPT'

uci add firewall rule
uci set firewall.@rule[-1].name='Allow-DNS-Surv'
uci set firewall.@rule[-1].src='surv'
uci set firewall.@rule[-1].dest_port='53'
uci set firewall.@rule[-1].target='ACCEPT'

uci commit
reboot

The above script broke my WAN: I had the flint 3 connected to the ISP, but no internet access anywhere.
Thank you so much for your kind help.