Maybe you're connecting to the wrong port. The default one is 7624, but sometimes INDI happens to use other ports, like 7625, 7626 and so on. See the screenshot below.
If that's not your case, please let me know more details about your configuration, like the Android version and where the server is (e.g. an Astroberry).
You should also try other INDI clients and see if you can connect remotely.