There can be cases when your hotspot is working (users are getting the right IP address), but for some users the splash page is not displayed automatically.
This behaviour is dependent on the manufacturer of the device / OS. Most modern devices have embedded captive portal detection. When the user connects to the Wi-Fi, the operating system checks if there is a working internet connection by trying to reach a specific website. If it's blocked it assumes that this is a public hotspot so it opens a popup browser window so the user can log in.
But not all operating systems are doing this functionality. Some are just displaying a notification so the user can click on an icon to open a browser. Some are not doing anything.
In this case the user has to manually open a web browser and enter an URL manually which starts with http:// . Like http://www.cnn.com . If the user enters a website which is using SSL, like google or facebook, he won't be forwarded to the splash page.
It is also possible that "Auto Login" is turned off for that specific network, on the user's device. Here is an article how it works on Apple iOS.