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/**
 * Gravity Wiz // Gravity Forms // Map GF Checkbox Field to ACF Checkbox Field
 * http://graivtywiz.com/
 */
add_filter( 'gform_post_data', function( $data ) {
	// Update "checkboxes" to your cusotm field name.
	$data['post_custom_fields']['checkboxes'] = serialize( explode( ',', $data['post_custom_fields']['checkboxes'] ) );
	return $data;
} );