Purchase Order in Magento 2 is a payment method used for the commercial clients. The wholesale customers registers their name, required order details, and pays the amount to generate a purchase order. The same can be used by them for paying for the orders when sufficient stock is available. This default functionality of Magento 2 makes it easier for the B2B store owners to do business online through purchase orders. However, sometimes the wholesale buyers may not have purchase order number ready, and may require to place the order using another payment method. Therefore, you may require a programmatic solution to make purchase order number optional in Magento 2.