Credit memo qty greater than returned qty

What causes this issue?

You are entering a credit memo for a purchase order item which is
flagged as a returns item. The quantity for which you are entering the
credit memo is smaller than the difference between the quantity
returned and that credited to date.
INCLUDE MM_IV_MELDUNGEN OBJECT DOKU ID TX

System Response

The system has established that the product of <ZG>(credit memo
quantity - quantity to be credited) x order price</> is larger than the
tolerance for quantity variances set in Customizing.

How to fix this error?

Check your entries are correct and make any necessary changes.
Copied from 081; adapted for returns

Error message extract from SAP system. Copyright SAP SE.