ios – How to create an offline hotspot to transfer data between iPhone and another device?

I have a hardware accessory that (annoyingly) instead of supporting Bluetooth, requires a WiFi hotspot in order to communicate with an iPhone.

Unfortunately I do not have tethering on my mobile data plan, and it seems foolish to pay for that feature when I don’t need the internet aspect of it.

Is there a setting or app for iOS that will allow me to create an offline hotspot that nearby devices can connect to?