Where can I enter the exchange rate when creating a PO from a negotiation?

When creating a Purchase Order from a negotiation whose currency is different from the ledger (base) currency, the PO defaults the conversion rate type to “User.”

In "Manage Common Options for Payables and Procurement" requires the rate type to remain as “User,” so changing the default rate type isn’t an option.

Where is the field where the exchange rate can be manually entered during the negotiation-to-PO creation process?

Thank you.