The Edit Item Information operation inaccurately lists 'thumbnailFile' as a valid parameter for ArcGIS REST API.

Workaround

Using 'name', 'iteminfo', or 'serviceItemInfo' works as long as 'thumbnail' is used rather than 'thumbnailFile'. However, a quick look at the documentation to view the parameter names causes confusion when the JSON result returns a success message, but the thumbnail does not update due to the 'thumbnailFile' parameter usage.

Steps to Reproduce