The difference cannot be posted (calculate book inventory first)

What causes this issue?

The procedure for supporting physical inventory during opening times in
plant &V1& and storage location &V2& is activated. Therefore, the book
inventories for the counted items in a physical inventory document must
be calculated at count time before the physical inventory differences
for these items can be posted. However, no book inventories at count
time have been calculated for any of the items counted in physical
inventory document &V3&.

System Response

The system will not allow you to post the differences for document &V3&.

How to fix this error?

Execute the calculation of book inventories at count time. Then you can
post the physical inventory differences.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.