Thank you, Adrian for your answer. I don't know why images work at all either!!! I know the code could be better but I am just experimenting things. When I use <?php echo $article->featured_image->url; ?> I just get the path to the image, the image name was not there, so it didn't work. That is why I used <?php echo $article->featured_image ?> right beside it... and it worked. Am I doing something wrong here?
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Putting 'first' did solve problem. Thank you for that, but the code you suggested did not work for me. As I said, in the output I got the path to the image, but not its name.
Thank you for quick answer.
Edit: I was really hoping that <?php echo $article->featured_image->url; ?> would return me that image url including its name. But id doesn't , is this normal?