WordPress WP Search with Algolia plugin - push custom fields to Algolia.

functions.php

<?php
/**
 * Push custom fields to Algolia.
 *
 * @param array $attributes
 * @param WP_Post $post
 *
 * @return array
 */
function iweb_algolia_product_attributes( array $attributes, WP_Post $post ) {

	// Bail if this isn't our product post type.
	if ( 'product' !== $post->post_type ) {
		return $attributes;
	}

	$sku = get_post_meta( $post->ID, '_cmb_sku', true );

	$attributes['sku'] = $sku;

	return $attributes;
}
add_filter( 'algolia_post_shared_attributes', 'iweb_algolia_product_attributes', 10, 2 );
add_filter( 'algolia_searchable_post_shared_attributes', 'iweb_algolia_product_attributes', 10, 2 );