A long time ago, I was unable to get a HotSpot working while using a SIM from LycaMobile (different phone, though, although that wouldn’t have mattered). Turned out their TOS specifically forbid sharing the internet connection and the provider had taken technical measures to prevent customers from doing so (which I finally was able to overcome).
So, yes, I second the reply from @cartron. First thing you should check is your mobile plan. It’s not unheard of that providers block tethering on a technical level.