1. The CSV Import file shouldcontain the same Item Name format as shown in Transactions> Sales> Enter Sales Orders > Items tab > Items subtab> Item drop down field.
2. Internal ID can also beused instead of Item Name. Just make sure that on the field mapping page, clickon the pencil icon beside the Itemfield and ChooseReference Type = Internal ID.
3. Verify if theItem is Inactive. If the Item record is inactive, set it to active statusbefore importing.

-Navigate to Lists > Accounting > Items.

-Check the ShowInactives box.

-Uncheck the Inactive boxbeside the Item Name.

-Click on Submit.

Yes it is possible by applying filters, in filter tab select relevant filters whatever you want.