Feedback app is down because of a fatal crash of my personal server some time ago. Haven't found the resources to replace it yet.
However, it is just a list of extensions like:
B4X:
Dim exts as List
exts.Initialize
exts.add("jpg")
exts.add("bmp")
exts.add("png")
FileManager.SetUploadOptions("/" & ABMShared.AppName & "/" & Name & "/abmuploadhandler", DownloadMaxSize, exts)