An SAP MM user can create a Purchase Requisition (PR) with ME51N transaction code (t-code). In SAP, the PR can be processed automatically into a Purchase Order (PO) with less effort by buyer/purchaser (which often the different party than the PR creator). But, to make this run well, there are some prerequisites that must be fulfilled before, which are:

• The PR item must contain a material number (which means there must be a material master data for the item).
• The “Automatic PO” indicator must be ticked for the material master (on the General Data section of ”Purchasing” view of the material master). You can check it with MM03/MM02 t-codes.
• The user must choose one of the possible sources at “source of supply” tab of the PR item (on ME51N/ME52N). The source can be an outline agreement or info record.
• The “Automatic Purchase Order” indicator must be ticked for the vendor master data of the source (on the purchasing data of the vendor). You can check it with MK03/MK02 t-codes.
• The source (outline agreement/info record) must be maintained and valid at the time of PO creation. You can create/update outline agreement with ME31K/ME32K t-codes. You can create/update info record with ME11/ME12 t-codes.
• Depends on your SAP PO screen layout configuration, you should make sure that all the required fields on PO can be populated either from material master data, vendor master data, or outline agreement/info record, such as terms of payment, incoterm, tax code, etc.
• After PR has been successfully saved (and released if needed), the buyer/purchaser or a background job can run ME59N t-code to create Purchase Order (PO) automatically. The PO can be created without the need of buyer/purchaser looking for possible sources as it has been chosen by the PR creator.