Purchasing -> Vendor Maintenance and Listings -> Vendor Maintenance (PO1202) -> Use the Look Up icon or enter the Vendor Number -> Enter D (Do Not Use) in the Status field
Marking the vendor as D (Do Not Use) this will make the vendor inactive. This will prevent KeyNet users from seeing that vendor in the vendor list when entering a requisition, as well as prevent Keystone Client users from accessing the vendor in any step of the purchasing/payment process.
The vendor can still be accessed in Vendor Maintenance, allowing access to the vendor history and the ability to make the vendor active again.
Another option is to mark the vendor as N (No Requisitions or POs). This removes the vendor from lookups for requistiions and purchase orders in both KeyNet and Keystone Client. However, you can still enter invoices against the vendor.