We are developing an application for a kiosk for printing pictures received through the WiFi from smartphones. For this we put a hotspot on a kiosk and when smartphone connects to it we open a captive portal web page which guides the user through the next steps.
The problem is that there is no Internet connection from this WiFi network and apparently some iPhone models (we noticed that with iPhone 5S in particular) try to access certain resources in the Internet and if unsuccessful they disconnect from the WiFi with "no Internet connection" error. At the same time, most of other models successfully open captive portal page without reaching out to the Internet.
Is there any specifics of some iPhone models or iOS version, or are there any settings that prevent iPhones working with captive portal without an Internet access? Maybe there is a certain resource it is trying to access and a certain response to receive, so if we configure the proxy to return expected response it will swallow it and continue without Internet?