Creating a Purchase Order involves a three-step process: Upload, Submit Process Requisitions, and Delete Process Requisitions. During the Upload step, records are placed in the "interface" web service. The Purchase Orders are then created during the Submit Process Requisitions step. The Delete Process Requisitions step is used to keep the "interface" clean.
While it is possible to execute these steps independently, it is highly recommended to combine them. By joining these steps together, you can streamline the process and ensure that all records are appropriately managed throughout the creation of the Purchase Order.