wordpress_ajax.php

//Setting Ajax handlers
add_action( 'wp_ajax_nopriv_get_author_info', array( $this, 'bps_get_author_info_cb' ) );
add_action( 'wp_ajax_get_author_info', array( $this, 'bps_get_author_info_cb' ) );

/**
 * Function used to get author info for popup on article
 */
public function bps_get_author_info_cb() {
	global $coauthors_plus;
	//Checking nonce
	check_ajax_referer( 'special-ajax-nonce', 'security' );

	$user_id = $_POST['author_id'];
	if ( ! $user_id ) {
		wp_send_json( [ 'error' => 'No user id found' ] );
		exit;
	}
	//Guest Author
	$curauth = $coauthors_plus->get_coauthor_by( 'id', $user_id ); //Getting user obj

	if ( ! $curauth ) {
		wp_send_json( [ 'error' => 'No user found' ] );
		exit;
	}

	//Guest author data
	$user_photo = get_the_post_thumbnail( $curauth->ID, 'user-thumbnail' );

	$response = array(
		'author_thumbnail' => $user_photo,
		'author_bio'       => $curauth->description,
		'author_nicename'  => $curauth->user_nicename,
	);

	wp_send_json( $response );
}