Differential invoicing: invalid unit of measure

What causes this issue?

You have activated the check for the credit memo quantity in
Customizing. The unit of measure referenced in the credit memo item of
the IDoc or the SOA message (&V1&) does not match the unit of measure
known to the system from the preceding invoice (&V2&).

System Response

The document was not posted.

How to fix this error?

Either deactivate the credit memo quantity check for your partner in
Customizing for <LS>Materials Management</>, under <LS>Logistics Invoice
Verification</> -> <LS>EDI</> -> <DS:SIMG.OLMROMRY>Enter Program
Parameters</> or ask your supplier to correct the unit of measure
required in the credit memo item of the IDoc or SOA message.

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.