Send email get_post_meta

Hello,I have a problem, after saving the entry I want to send an email. two email are sent correctly but $friendemail=get_post_meta( $post_id, 'alerta-emails', true ); is emprty.

Thanks

array(
	'id' => $prefix . 'emails',
	'type' => 'email',
	'name' => 'Email',
),

function send_mails_on_publish( $new_status, $old_status, $post_id)
{
	$post=get_post($post_id);
	
    if ( 'publish' !== $new_status or 'publish' === $old_status
        or 'alertas' !== get_post_type( $post ) )
        return;
	
	$friendemail=get_post_meta( $post_id, 'alerta-emails', true );
	
	if( 'true' == get_post_meta( $post_id, 'alerta-emails', true ) )
        return;

    $author = get_userdata($post->post_author);
    $admin= get_bloginfo('admin_email');
    $emails      = array ($admin, $author->user_email, $friendemail);
    $alert = "Detalle". $post->post_title; 
    wp_mail( $emails, 'Nueva alerta publicada', $alert );
}