You can mark an order as Delivered only after its status is updated to the right stage.
If the order is from the Head Office, the status has to be first set to Fulfilled by them when the stock is sent to you. After that, you can change it to Delivered.
If the order is from an outside vendor, the status must be marked as Paid first. Once it is Paid, you can then change it to Delivered. If the order is from an outside vendor, the status must be marked as Paid first. Once it is Paid, you can then change it to Delivered.