Confirmed quantity & less than delivered quantity & for PO item & &

What causes this issue?

You have attempted to transfer the quantity confirmed by the supplier
&V1& into the schedule lines of PO item &V3& &V4&. The quantity &V2& has
already been delivered against this PO item. The confirmed quantity may
not be less than the quantity already delivered.

System Response

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

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.