I released a proof of concept Android app that lets you buy/sell wifi access and pay/get paid with Lightning.

When app is enabled it listens to connection requests from other devices via Android Nearby API which uses Bluetooth, wifi direct etc.

When buyer requests wifi access, seller enables the hotspot and sends over WiFi details along with a lightning invoice. Buyer connects to wifi and pays the invoice.

Taking payment works with opennode.co.

LightSpot on Play Store