A connection to a lightning charge node or clightning unix socket is required to generate lignting network enabled invoices. This is experimental and not advised for production so keep in mind:
You might lose your money
The devs of BTCPay Server don't know what they are doing and won't be able to help you if shit hit the fan
You approve being #reckless and being the sole responsible party for your loss
BTCPay Server relies on a Lightning Charge node or CLightning unix socket
If you have no idea what above mean, search by yourself
If you still have no idea how to use lightning, give up for now, we'll make it easier later