A document style is a template that defines the layout and content of a purchasing document, such as a purchase order, a purchase agreement, or a requisition. You can create a document style that supports credit lines, which are purchase order lines with a negative amount to record credits to the ordered amount that you have negotiated with your supplier. For example, you can use a credit line to represent credit for an equipment trade-in. You can also specify other attributes for the document style, such as the line types, the change order policies, the approval rules, and the communication methods.
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How You Create Purchase Order Lines with Negative Amounts
How You Enable Creation of Purchase Order Lines with Negative Amounts
Create Supplier Contracts from Negotiation Award

Page Composer is a tool that you can use to customize the user interface of Oracle Fusion Cloud Procurement applications by adding, removing, or rearranging fields on pages. You can also modify the properties and styles of the fields, and add flex fields and hyperlinks. To make the negotiation details field available for Purchase Orders and Purchase Agreements, you can use Page Composer to edit the page layout and add the field from the source pane. You can also specify the conditions and expressions for displaying the field.
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Modify the Requisitions Page Layout Using Page Composer, Section 1: "Modify the Requisitions Page Layout Using Page Composer" Page Composer, Section 1: "Page Composer"