You have already recorded an item for material & supplier &

What causes this issue?

The material has been assigned step-by-step release for the supplier.
However, you have already recorded an item for this material/supplier
combination.

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?

Cancel this item.

Error message extract from SAP system. Copyright SAP SE.