Product prices from a contracted product catalogue that has been uploaded by a Formal Supplier can only be changed on the Supplier's end. Each Supplier has their own pricing structure, which is not governed by Purchase Plus.
However, the prices can be changed;
if the Purchase Requisition is an Informal Requisition. The product and price can be amended accordingly prior to submitting the Requisition for approval. Please check out this article for more information, Create an Informal Requisition.
If the product is from a Creating a Self Managed Pricing Catalogue, the price can be changed by the User in the Self Managed Catalogue before raising a Purchase Requisition. [Note - the price cannot be changed whilst raising a Purchase Requisition].