The main EAN for the supplier & and unit of measure & is not unique

What causes this issue?

You wanted to assign additional
<DS:GLOS.International_Article_Number>EANs</> to the supplier &V1& and
to the unit of measure &V2&. You have entered several EANs for the
supplier and for the unit of measure, but the main EAN is not unique
since more than one EAN is flagged as the main EAN.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Correct your entries by flagging one EAN as the main EAN.

Error message extract from SAP system. Copyright SAP SE.