Target quantity &1 &2 and transaction quantity &3 &4 have opposite signs

What causes this issue?

The Quantity Conversion Interface (QCI) converts a transaction quantity
(at a given UoM) into a table of target quantities at requested units of
measure. The target quantity and transaction quantity have to be either
both positive or both negative. This is not the case.

System Response

The system stops processing. For goods movements, negative quantities
are not allowed, except for difference postings calculated from physical
inventory postings.

How to fix this error?

Adjust either the transaction quantity or target quantity sign.

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.