Problem:
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Customer Order
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Solution: We have Customer Order including 3 items:
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was partly invoiced, but a new Invoice contains full amount of the order.
Solution: Check Hierarchy Structure of the documents and their chronological order (dates and time should follow).
1. Customer Order contains three items:
2. One Invoice is already posted and contains 2 of 3 items:
But while generating of the 2nd invoice second Invoice for the remaining item, the system is including includes all items in a new invoice , not only the remaining itemone:
The issue is caused by the date of the 1st invoice, it 's is preceding the 2nd invoice.
In the above example 1st , the first invoice is posted on December, 05/12/2022, but 2nd the second invoice is being created on 04/12/2022. But if you create December, 04.
As the system find no sales before December, 04, then it considers as total amount as not invoiced.
3. Create invoices subsequently, the system will show you shows only the remaining items and qty that have not been invoice yet not invoiced Quantity based on this particular Customer Order: 
Thank you for being a FirstBIT customer!
# partial invoice customer order based