In Migration Cockpit, migrating Material Inventory Balance template, the following message error is shown.
"Tab Material Document Item, field Entry Quantity, is empty; enter value for the mandatory field"
In Material Inventory is not possible perform Good movement with quantity 0 (zero).
Field Entry Quantity is empty or was filled with value equal to 0 (zero).
Accordingly with field tip, you can fill it with quantity 1
"Enter the quantity for goods movement posting. Note: if your material is using serial numbers please enter quantity 1 for each serial number"
After migration it is possible to "clean" quantity 1, there exist Scrap Movements, that can be post with following applications, reducting from 1 to 0, or you can create Physical Inventory to material and inform the invetory is 0.
Refer also to Material Inventory Balance sample, available in SAP note below:
Good movements, Entry Quantity, Material Inventory Balance, Migration Cockpit , KBA , CA-GTF-MIG , SAP S/4HANA Data Migration Cockpit Content (LTMC) , MM-IM-CNT , S/4HANA Inventory Management Content , Problem