order.status = "completed" not updating the status

[kmchow3]

Wordpress version: 5.8, WooCommerce version: 5.6.0 and WooCommerce.NET version: 0.8.2

Anyone has any idea why it cannot update the status of an order object? The statement runs fine and doesn't generate any error, but the status just doesn't get updated, i.e. stays at "processing".

wcorder.status = "completed";