Most have a charge/data charge for using such. Just an example in the link below:
https://www.verizonwireless.com/archive/mobile-living/tech-smarts/how-to-use-your-smartphone-as-a-mobile-hotspot/
Verifying your data charges on your phone might explain it all.
Hope this helps.
Grif
I have discovered the mobile hotspot option on my Lenovo ideapad (windows 10) I wondered if I was to connect my phone up to it , would it be free or would I have to pay?.

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