When the material is shipped in advance and the invoice is issued afterwards, an invoice dispatch connection is established, eliminating the need for re-entering dispatch information. 
In order to transfer dispatches to invoices, you can use Transfer Receipt / Dispatch option in the Operations menu in invoices or Bill option located in F9 - right click menu of dispatch lines.

Transferring Dispatches

The "Transfer Dispatch/Receipt" option is used to transfer dispatches into the invoice collectively. It is located under Operations menu in dispatch.
The filter options located in the Dispatch/Receipt Transfer Transactions window are used to specify the dispatches to be transferred to the invoice. The filter options are:

Slip Dates

Start - End

Trading Group

Group / Range

Dispatch/Receipt Document No

Group / Range

Document Dates

Start - End

General Discounts / Expenses

Transfer / Do Not Transfer

Slip Dates: This filter line is used to enter start and end date in order to list the dispatches belonging to the AR/AP of the invoice. 
Trading Group: Used to filter dispatches to be billed by trading group. 
Document Number/Date: Dispatches to be billed can also be selected by document number and date. This filter is used to list dispatches by document numbers and date info. 
General Discounts / Expenses: Used to determine whether the discounts and expenses incurred in the dispatch will be transferred into the invoice. 
While billing dispatch, all changes applied in invoice, discount/ expense/promotion lines applied to the material line reflect to the dispatch as well. Material/discount/promotion lines which are deleted from invoice are also deleted from the dispatch. However, a new dispatch record is generated for promotions added to the invoice (general). Discounts and expenses applied to the invoice (general) do not affect related dispatches. 

Listing Dispatches Transferred Into Invoices 
During invoice entry or old invoice control transactions, dispatches on the invoice are accessed through the Dispatches option on invoices. Dispatches on the invoice are listed along with number, dispatch type, date and description information. 
In cases where the invoice and the dispatch will be printed with the same date, the Dispatch Date can be changed. The change made here is automatically transferred to the dispatches. Dispatches transferred into invoices are displayed on the sales dispatches list with a check indicating that they are billed. Billed invoices can be displayed on the sales dispatches list only for viewing purposes. The Sales Invoices section can be used for the changes to dispatch information or removing the dispatch from the records.

Billing From Sales Dispatches List

Sales dispatches can also be billed from the dispatch list. This transaction is performed using the Bill option located in the right click menu of the Sales Dispatches List. The Bill window is displayed, allowing invoice information to be viewed and recorded.