Well, the forum rules (see FAQ) clearly says you should post the result of your best try and mention why the outcome is not as you expected. Furthermore the help is available on the forum and there’s also a guide so I suggest you read that guide and you search the forum as there are several topics showing examples of custom reports.
As per the FAQ, if you want help with custom reports, you need to post the definition of your best attempt and a screen shot of the results. @Mark already called your attention to this guidance. You ask “why,” but how could anyone know without seeing your report definition?
I would temporarily add the General Ledger Account/Name to the Select clause and remove the Where clause to see that there are actually any transactions for the period and Inventory-Sales accout for the period
It is better to start with many more transactions than you want and once you are sure that the transaction you want are in the list, eliminate those you do not before doing the sorting and grouping
Please read the forum rules FAQ - Manager Forum and posts above referring to the same. Especially read:
If your question is related to custom themes or custom reports, always post the code or report definition you have developed and the results it produces. Do not simply post a picture of something you want and ask other users to tell you how to achieve it.