The invoice screen represents a single invoice in the system. For purchases, the invoice should reflect the invoice you receive from your supplier. For sales, the invoice is the document that you will send to your customer.
Material from multiple contracts can be applied to a single invoice. However, an invoice will always carry an association with a single purchase contract (and a single sale – for sale invoices), the contract that was selected when the invoice was created.
Entering invoices are the mechanism by which material purchases and sales (as well as vendor payments) hit the G/L. The invoice will not affect the G/L (and the material will not show as paid for) until the invoice is posted. A posted invoice cannot be edited or altered in any meaningful way. To make a modification, you must create a new invoice that supersedes the posted invoice.
Before you can post an invoice, it must first be printed and reviewed.
Information on the above Invoice Screen:
PROVISIONAL
.A posted invoice has a different set of options available, mostly because you cannot edit or substantially modify a posted invoice.
The unposted invoice has additional options related to editing or altering the invoice.