Unit of measurement &1 in PSA assignment not valid for product &2

What causes this issue?

An entry exists for the product &2 in the table /SCWM/TPSASTAGE.
(Transaction /SCWM/PSASTAGE).
The unit of measurment &1 in this entry is not valid for product
&2

System Response

The system does not use the unit of measure and the quantity proposal.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.