I'll start with the full disclosure that I am not pro on the RuckOS yet but from what I have seen, when the only option you are given in a drop box is "reload" it means that you need to configure an object that would populate that dropdown. Since the local database drop down gives you only the reload option, I'd guess that you need to create that local database. I wish I could be more helpful and tell you how to do that but here's hoping you may have seen the option or something related to it and this just serves as the brain trigger to do it.
Local DB is an option for authentication, not captive portal. In order to chose a captive portal as an option you first have to create such portal under the Hotspot (WISPr) and select Logon URL as Internal. This will allow you to setup your T&C and some other features there as well. This will also let you setup a logo for your portal.