One of these will definitely do the trick

If your Android hotspot turns off automatically, your connected devices won’t be able to access the internet. This issue usually occurs when you enable a mobile hotspot settings option. There are other causes as well, and we’ll show you how to fix it.

Other reasons why you may not be able to use your hotspot include your phone having battery saver mode turned on, you exceeding your internet data usage allowance, incorrect network settings, and more.

Whenever you are facing issues on your phone, the first solution that you should apply is to restart your phone. This will force your phone to end all open services and apps, and fix any minor issues with those items.