§ 01
Definition
The network intercepts your first web requests and redirects them to its own page until you accept terms, enter a room number or pay. RFC 8952 describes how captive portals should work, and modern phones detect them automatically.
§ 02
How it works
Because the portal blocks normal traffic, a VPN usually cannot connect until you have signed in. A strict kill switch or 'always-on, block connections without VPN' setting can stop the portal page loading at all, so you may need to pause the VPN briefly, sign in, then reconnect.
§ 03
Why it matters
The minutes before you reconnect the VPN are when your traffic is exposed to the network. Sign in, reconnect immediately, and avoid entering passwords or card details on the portal page beyond what it needs.