CSV Import of Sales Order generates “Invalid Opportunity Reference Key xxx for entity xxx”

Answer/Solution:
1.Navigate to Transactions> Sales> Enter Sales Order
2.On the Customer field, select name of the customer
3.On the Opportunity field, ensure the opportunity is listed.
          -If listed, copy the format and paste it on the CSV file to re-upload the file.
          -If not listed, verify the status as system only associate Opportunity with Open Status.

Note: To confirm the status, navigate to Transactions > Sales > Create Opportunities > List and click View on the Opportunity record