How to develop applications for Smart Signage devices?

Hi, I have a QM55R Smart Signage TV. I want to develop an application to download required files, store them and then open html file. I tried to create native app using .NET but my tv has tizen 4.0

I upgraded my firmware but it still tizen 4. I think I should to create web app and use tizen api's for reach filesystem or download files etc. But tizen api's does not work. Can I use tizen api's on Smart Signage tv's? My tv has no apps menu or app list. It just has url launcher or magicinfo.