I'm dealing with a Raspberry Pi 3 that is using hostapd to create its own wireless network.
When an Android client first connects to the network, it tries to grab the page
http://connectivitycheck.gstatic.com/generate_204 to see if it's behind a client portal. My Raspberry Pi redirects this request to an instance of nginx that it is running, and returns a 302 redirect to my login page.
Because Android didn't get the response it was looking for (an HTTP 204), but got a 302 instead, from what I understand, it's supposed to popup my login page. I've seen this in action using other captive portal hardware.
In my case however, Android just shows a popup that says "Internet may not be available: Connect to another network or turn on Switch to mobile data".
Am I doing something wrong? Is there something specific Android is looking for in the login page before it will make it pop up?
Most of my testing is on my Galaxy S8. I tried it on a friend's S9, and that doesn't work either. Using a Windows 10 laptop though, the login page does popup.