Woocommerce set Guest shipping_postcode on homepage

Hi,
I have Australian woocommerce website on which I have created an postcode pop up at home page. Now Guest will provided its post code or zip code then its respective shipping tax would be get applied at checkout page. I have different shipping rates based on post code.
I applied following code but its not working

add_filter( ‘woocommerce_checkout_fields’ , ‘custom_override_guest_shipping_checkout_fields’ );

function custom_override_guest_shipping_checkout_fields( $fields ) {
$fields[‘shipping’][‘shipping_postcode’][‘default’] = ‘2150’;
$fields[‘shipping’][‘shipping_country’][‘default’] = ‘AU’;
return $fields;
}

Feedback appreciated