Surface unit of measure & does not exist (Correct)

What causes this issue?

The surface unit of measure &V1& has not been defined.

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?

Enter the correct surface unit of measure
or
choose a surface unit of measure using the F4 function.

Error message extract from SAP system. Copyright SAP SE.