Fulfillment tab/page fields on a Contract for a CPA

Summary: Hello experts, when I am trying to create Fulfillment lines on a contract to be used for a CPA the Supplier field is not able to be populated which is a required field for the 'Create Agreement' selection/process on the Fulfillment line (once created). This is for contracts that are pulled into Oracle from an integration process.

If I manually create a contract I am able to enter in Buyer, Supplier, Supplier Site on the fulfillment line details under the Purchasing header area as the fields are all active and allow input. But for all contracts that come over as Active from our integration I cannot seem to edit and the Supplier field is not an active field that allows input. Which then causes an error when trying to use the Create Agreement from the Fulfillment Actions menu. See screenshots.