@OmadaSMS 

Hey

Personally I wouldn't have set the DNS on the AP or OC200, the DNS on these I would have left as your Gateway / Router (whatever it is).   Instead setting the DNS on the gateway / ISP Router or whatever you have.

@OmadaSMS 

Set the DNS servers on your router. 

I have a similar set up with EAP's and the OC200 controller. 

On the router I set Cloudflare DNS servers, that block explicit sites and malware. 

Thanks @rjow2021 

The installs are all captive portals behind customer routers that we don't have access to.  Setting DNS in the router is not an option.

What is the purpose of the DNS settings in the OC200 and EAP if they don't do anything?

@OmadaSMS 

Its incase you have 2x or more DNS servers on your network, the same can be seen on windows devices also.

Say I have 3x DNS servers,  192.168.1.1     192.168.10.2     192.168.20.3      

Typically you would not put the external DNS on anything but the WAN facing router itself.   On clients or internal hardware (PC, laptop, OC200, APs etc) the DNS will always be the router / gateway.    Putting a DNS on the OC200 wont work as the gateway will just ignore and fire the packet to its DNS..  

The purpose of the DNS on these devices is to point it to which DNS server you wish it to use, say 192.168.10.2  in our example.   These are generally internal DNS servers and not the WAN DNS

Just to state the obvious, your preference for DNS servers needs to be set on your router / gateway -- or whether your DHCP clients lease their IP's from. -- Adjusting these settings on the OC-200 / EAP's will not do what you want.