Order status won’t update to custom status

Hi I have a paid version of Custom Order Status.

In my functions.php file if the user pays I’m trying to set the status to a custom status in these hooks.

It does return those values correctly (i.e. the if statement is satisfied) but the order status never gets updated:

add_action( ‘woocommerce_payment_complete’, ‘so_payment_complete’ );
function so_payment_complete($order_id){
$order = new WC_Order($order_id);
if($order->has_shipping_method(‘uk_flat_rate’) || $order->has_shipping_method(‘uk_free’)) {
//update order status to UK Status
$order->update_status(‘uk-status’,”,true);
}
}

add_filter(‘woocommerce_payment_complete_order_status’, ‘so_update_order_status’, 10, 2);

function so_update_order_status( $order_status, $order_id ) {
$order = new WC_Order($order_id);
if(($order->has_shipping_method(‘uk_flat_rate’) || $order->has_shipping_method(‘uk_free’)) && $order->get_status() != ‘uk-status’) {
//update order status to UK Status
return ‘uk-status’;
}
return $order_status;
}

Regardless of either of these methods being hit the order status is always set to On Hold instead of the defined custom status.

Any ideas why?