Background image UIButton

Hi everyone!

I set the image to the background for the button via setBackgroundImage(), but nothing happens. I tried with images of different formats, it doesn't help.
At the same time, the background is placed in the inspector, but not through the code.
What could be the problem?

` @IBOutlet weak var button: UIButton!

override func viewDidLoad() {

button.setBackgroundImage(UIImage(named: "eu"), for: .normal)