Not able to add lumpsum discount either amount or percentage on Sales order total value

Summary:

We have created a sales order of certain amount, now we need to add a lumpsum amount or pecentage base discount on sales order total value or say a header level discount

Content (please ensure you mask any confidential information):

We have created a sales order of certain amount, now we need to add a lumpsum amount or pecentage base discount on sales order total value or say a header level discount

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