The material availability check is crucial before placing an order in process. Settings for order type and material master determine whether a material availability check is possible, how it should be run, and how shortfalls should be dealt with.
Material Availability Check: Settings and Features

The availability check leads to a shortfall (FMAT) status being generated when there is a deficit in the warehouse. You can determine whether or not an order is allowed to be released despite shortfalls.
Availability checks can be set to generate a dynamic check of all goods received and goods issued (order requirements, orders, stock in transfer, safety stock, and so on).
These settings are determined for the combination of checking group and checking rule.
The checking rules are then assigned to the order type. The checking group is recorded in the material master.
Component List (SAP GUI)

The component list of a maintenance order can be changed using its own transaction (IW3K). Supplements and changes can thus also be made by employees who have no change authorization for the order.