Works for me - bridge@EWC, V10.21.02, AP3705i, in my case I've blocked traffic as that was easier to test.
Note: it took some minutes before the traffic was blocked so I'm not sure whether I've done something wrong or whether there is some sync happening until it's active.
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Have you enabled application visibility on the WLAN service ?
Back to the overall goal...I'm not sure whether I unterstand the setup..
the WLAN service is set to authentication for external captive portal and the screenshot show the unauthenticated traffic role ?
And then in case someone uses facebook, mail it should redirect to the portal and the user needs to authenticate on the portal ?