Hi JuliaL
Can I have a little more clarification on what steps you are taking - Is this item marked as I sell and I inventory, or just I sell? As you mentioned that the item is non-inventoried, but when I have a look at the Selling Details screen, it only shows Number of units if the item is marked as an inventoried item.
If it is inventoried and you have entered a sale then you will not be able to change the Number of units. The only way to change it is if you delete all the sales first.
Hope that helps, and if you have further questions, I would still require a screenshot of the item and the error message, to help me understand the exact issue.
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