When trying to use kiosk following error is shown: "Several categories are missing" And no wallpapers are shown.
Can you be more specific? What "Kiosk" are you using, are you talking about Kiosk Restrictions? What exactly did you do? Where do you get that error? ...
Settings->Arbeitsfläche->Wallpaper->Click "Download new wallpapers"->Error
Thanks. So, this has nothing to do with Kiosk Restrictions then.
Which version of KDE Frameworks are you using? At the moment there is a conflict between the server side of GHNS and KDE Frameworks 5.23. It should work with both 5.22 and 5.24.
I have the same issue -- no response beyond "some categories not available" from the Get Hot New Stuff dialog for "Get New Wallpapers". Re Thomas Pfeiffer's comment in #4 though I have (via "sudo apt list plasma-framework") the latest framework for Kubuntu 16.04, namely "plasma-framework/xenial,now 5.23.0-0ubuntu1~ubuntu16.04~ppa1 amd64 [installed]". Neither 5.22 nor 5.24 are available to me via apt repos I have (which are the standard Kubuntu ones plus a few extras). FWIW it appears that you can get the content direct from https://store.kde.org/.
This bug may relate to https://bugs.kde.org/show_bug.cgi?id=348049 ?
This is a known problem with KDE Frameworks 5.23 which was fixed in 5.24. Please ask your distribution to ship at least KDE Frameworks 5.24.