If you can't see the location portal after connecting to the hotspot, there are a couple of possibilities:
Your network configuration doesn't allow the traffic through. Check if your tunnel if set up correctly by looking at this article
Your device doesn't allow Wi-Fi popups. It is usually due to a setting being turned off in the Wi-Fi settings, changing the default behavior of the device. Try to connect to a regular HTTP address in your browser, the redirect should operate and the portal will be displayed. Please note HTTPS addresses will not redirect to the portal.