Error when trying to set access permissions of file owned by user

I'm trying to copy the access permissions of a source directory to a destination directory. The Finder Info panel of the source directory shows the following permissions:

• Source directory:
  • I: Read & write
  • Everyone: No access
• Destination directory:
  • I: Read & write
  • Staff: Read only
  • Everyone: Read only

The following code succeeds in creating a file in the destination directory, but then fails when setting the URL.fileSecurityKey resource:

let openPanel = NSOpenPanel()
openPanel.canChooseDirectories = true
openPanel.canChooseFiles = false
openPanel.runModal()
let source = openPanel.urls[0]
openPanel.runModal()
var destination = openPanel.urls[0]
do {
    try Data().write(to: destination.appendingPathComponent("asd"))
    try destination.setResourceValues(source.resourceValues(forKeys: [.fileSecurityKey]))
} catch {
    fatalError(error.localizedDescription)
}

The error message is:

You don’t have permission to save the file “destination” in the folder “parent”

I thought that an app run by a user has the same permissions as the user itself, and since I have read & write access to both the source and destination directories, the app should be able to copy the access permissions without issues. What is the problem?