In this step you are going to define the scope and interface structure of the BAPI, that is, the individual import, export and table parameters required for calling the BAPI. You will specify the names of these parameters in the sectionNaming Parameters in the Function Module.
You cannot use change and exception parameters in a function module which implements a BAPI.
Try to structure the BAPI as clearly as possible. Match the import parameters with each other to avoid having redundant data in the interface.
To identify the interface parameters for your BAPI, proceed as follows:
For example, this could be a customer number (CustomerNo) in the BAPIs Customer.GetDetail() and Customer.CheckPassword(), or the number of a sales document in the BAPI SalesOrder.GetStatus().
These BAPIs return one key value, for example, an order number in the BAPI SalesOrder.CreateFromData().
Class methods are instance-independent and are called without the use of key values. Usually they return a table with a selection of key values. Exceptions are write BAPIs, as described in the list item above.
You have to create an export parameter, Return, to send messages back to the calling program. For details, see