With Hotspot FREE SPLASH you have to include the login form in your HTML using an iframe. This is described in the guide, step 3: http://www.hotspotsystem.com/deskpro/kb_article.php?ref=3635-EGXV-1011

You can also skip this part if you don’t want to provide internet connection at all, but you want to use the wifi for advertising your product or services.

In what form did you put multiple domains in the uamallowed field? It should be like:

http://www.domain1.com,www.domain2.com