In the integration between SAP Ariba Buying and Invoicing and an SAP ERP or SAP S/4HANA system via the Managed Gateway for Spend & Network, the real-time budget check is performed on the purchase requisition. When a user creates or submits a requisition in the SAP Ariba solution, a synchronous call is made to the backend SAP system to validate the availability of funds. This pre-emptive check ensures that the requested expenditure is within the allocated budget before the requisition is approved and a legally binding purchase order is created, thereby preventing budget overruns.

A. Purchase order: The budget is typically reserved or committed during the requisition approval phase. The purchase order is created from an already budget-checked requisition, formalizing the commitment.

B. Invoice: An invoice is a request for payment against a commitment already made by a purchase order. Performing a budget check at this late stage would be ineffective for budget control.

D. Advance payment: An advance payment is a payment transaction against an existing purchase order. The budget commitment has already been established and checked before this stage.

1. SAP Ariba Cloud Integration Gateway Documentation: The official guide, "How to configure real-time budget check," explicitly details the process. It states, "The real-time budget check feature allows users to check for the availability of funds in the SAP ERP or SAP S/4HANA system when they create requisitions in the SAP Ariba solution."

Source: SAP Help Portal, SAP Ariba Cloud Integration Gateway, "Configuration for SAP Ariba Buying and Invoicing," Section: "How to configure real-time budget check."

2. SAP Ariba Buying and Invoicing Product Documentation: The process flows for integrated procurement consistently show the budget check as a step within the requisition approval workflow.

Source: SAP Help Portal, SAP Ariba Buying and Invoicing, "Managing budgets," Section: "Budget checks in the procurement process." The documentation describes how budget checks are integrated into the requisitioning process to control spending.