Credit memo qty smaller than GR qty

What causes this issue?

The quantity for which you are entering a credit memo is smaller than
the quantity returned to date minus the quantity credited to date.
INCLUDE MM_IV_MELDUNGEN OBJECT DOKU ID TX

System Response

The system has found that the <ZG>(quantity to be credited - credit
memo quantity) x order price</> is greater than the tolerance for
quantity variance set in Customizing.

How to fix this error?

Check your entries are correct and make any necessary changes.
Copied from 194 and modified for returns

Error message extract from SAP system. Copyright SAP SE.