Then I would check internet connection on Android, to see if the phone can access internet itself. Not sure but there could be some Internet sharing feature that's disabled on Android ? just a guess
Once that's ok, if there is any issues then it's iphone setting.
Make sure the distance between the two phones is short, even when the WiFi bars are showing good signal, in my experience using hotspot you must:
- have both devices close to each other
- make sure the one that's providing Internet is getting good LTE (4G) reception and it is able to browse the web.