No EAN references maintained for material & in sales unit &

What causes this issue?

A regular change or a change with a future validity date has resulted
in the EAN for the sales unit of this material being deleted. Either
that or the EAN was not maintained when the sales unit was maintained.

System Response

The record could not be prepared for POS outbound.

How to fix this error?

<DS:TRAN.MM42>Maintain the EAN for the material &V1& for the sales unit
&V2&</>.

Error message extract from SAP system. Copyright SAP SE.