Wordpress - get the attachement url for the medium sized image

wp_get_attachment_url() will only return url to original attachment file, this function only accepts attachment id as parameter.

Use wp_get_attachment_image_src() or wp_get_attachment_image() instead.

echo out the following: wp_get_attachment_image_src( $post->ID, 'medium')[0]; to the attachment url for the medium sized image.