CoAuthorsExtend.php

<?php
//Add guest authors metaboxes
add_action( 'add_meta_boxes', array( $this, 'bps_add_metaboxes' ), 10, 2 );
//Adding custom fields to guest authors
add_filter( 'coauthors_guest_author_fields', array( $this, 'bps_filter_guest_author_fields' ), 10, 2 );
 
/**
 * Adding metaboxes
 */
public function bps_add_metaboxes() {
	add_meta_box(
		'coauthors-manage-guest-author-test-info',
		__( 'Add header image', 'co-authors-plus' ),
		array( $this, 'bps_metabox_manage_guest_author_test_info' ),
		'guest-author',
		'normal',
		'default'
	);
}
	
public function bps_filter_guest_author_fields( $fields_to_return, $groups ) {
 
	if ( in_array( 'all', $groups ) || in_array( 'name', $groups ) ) {
		$fields_to_return[] = array(
			'key'   => 'job_title',
			'label' => 'Job title',
			'group' => 'name',
		);
	}
	
	if ( in_array( 'all', $groups ) || in_array( 'contact-info', $groups ) ) {
		$fields_to_return[] = array(
			'key'   => 'twitter_handle',
			'label' => 'Twitter handle (Without @)',
			'group' => 'contact-info',
		);
	}
	
	return $fields_to_return;
}