How to restrict users from being able to create a fulfillment/BPA that exceeds the contract amount?

Summary:

Currently, when creating an enterprise/procurement contract - on the overview page, you can specify the agreed amount. However, on the fulfillment tab, it allows users to create agreements which surpass that agreed amount. How can we restrict users from being able to create a fulfillment/BPA/CPA that exceeds the contract agreed amount? example: Agreed Amount $10,000 on overview page, fulfillment tab BPA/CPA amount $20,000, no error or hard stop which lets user know the fulfillment is more than the agreed amount at overview level.

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