Explanation
Purchase-order-based invoice verification is a process of verifying and posting an invoice with reference to a purchase order. Some key features of this process are:
The system proposes the quantity to be invoiced as the difference between the total delivered quantity and the total quantity already invoiced. This ensures that you do not pay more than what you have received.
Partial deliveries for a purchase order item are NOT flagged as individual invoice items. This means that you can post one invoice for multiple partial deliveries of the same purchase order item. References:
[SAP S/4HANA Sourcing and Procurement | SAP Learning], Course S4515, Unit 1, Lesson 1.

Explanation
When you create a blanket purchase order for several minor repairs that may occur during the year, you must enter the following data:
An account assignment category, which determines how the costs for the repairs are allocated to an account assignment object such as cost center or order.
An overall limit value, which specifies the maximum amount that can be invoiced for all items within the validity period of the blanket purchase order. References: SAP S/4HANA Sourcing and Procurement
| SAP Learning, Course S4520, Unit 2, Lesson 1.