Wifi end users purchasing data before being able to use

@nick.gavin, base on the requirement description, it looks like the InControl 2 > Captive Portal, [Token] access method might be applicable to the scenario. You can refer to this KB article for more details on configuring this option.

Of course, the customer would need a way (manually or 3rd party system) to take care the billing to the onboard passengers who use the Internet service.