For a client I'm working for, I need to be able to set the header background-image (so behind the menu if you have that set at the top) for a site (or just Home.aspx) because I only use the Home.aspx file. There are no other used files on this site.

I've tried getting there via the CanvasContent1 property like so:

_api/web/getfilebyserverrelativeurl('/sites//SitePages/Home.aspx')/ListItemAllFields?$select=CanvasContent1

But cannot find any background image property. Also tried looking at this endpoint, but I cannot find any documentation or a POST endpoint:

_api/siteiconmanager

Any help is appreciated!

-Stijn