There are two different failures here and they have different causes. Work out which one you have before trying anything.
- The other device cannot see or join the hotspot at all.
- The other device joins but no page loads.
It joins but nothing loads
This is the common one, and the answer is usually that your own phone has no working internet to share.
- Test the phone itself. Turn Wi-Fi off on the phone and open a web page over mobile data. If that fails, the hotspot was never the problem; go to the APN guide.
- Check the bundle. Some bundles, especially the cheap social or night ones, are not allowed to be shared. The network blocks tethering on them specifically. A normal data bundle will work where a social bundle will not.
- Check whether your plan allows tethering at all. Ask your network. Some prepaid plans exclude it.
- Turn the hotspot off and on, then reconnect the other device.
A laptop connected to your hotspot can pull a very large update the moment it gets online. If your bundle emptied straight after connecting a computer, that is what happened, not a fault.
It will not connect at all
- Check the password. The hotspot password is not your Wi-Fi password. Open Settings, Connections, Mobile Hotspot and Tethering, Mobile Hotspot, and look at it. Retype it on the other device carefully.
- Check the band. This is the fix people never find. If your hotspot is set to 5GHz and the other device is older, it cannot see the network at all. In the hotspot settings look for Band or AP Band and set it to 2.4GHz. It is slower and it reaches further and everything supports it.
- Check the hotspot is not hidden, and that the device limit has not been reached. Most phones cap it at eight or ten connections.
- Rename the hotspot to something short with no emoji, spaces or unusual characters. Some devices choke on those.
- Forget the network on the other device and join again fresh.
On an iPhone
If Personal Hotspot is missing from Settings entirely, it is usually the carrier profile. Check Settings, General, About for a carrier update, and confirm your APN is set, because the hotspot option disappears when the phone has no data configuration.
Also check Maximise Compatibility inside the Personal Hotspot screen. Switching it on forces 2.4GHz, which fixes most cases of an Android device or older laptop not seeing the iPhone.
Still nothing
Reset network settings on the phone. Android: Settings, System, Reset, Reset network settings. iPhone: Settings, General, Transfer or Reset, Reset Network Settings. You will lose saved Wi-Fi passwords and nothing else.
If the hotspot then works for one device but not another, the problem is the other device, not your phone.