EAN cat.&: check digit will be created for EAN & poss.assigned internally

What causes this issue?

You have set the indicator for determining the check digit
automatically. However, the corresponding field already contains an EAN
with EAN category &V1&.

System Response

The system cannot tell whether the EAN has been entered manually or
already assigned internally. When you select <LS>Enter</>, the system
will determine the check digit and add it to the EAN.

How to fix this error?

Make sure that this is what you intend.

Error message extract from SAP system. Copyright SAP SE.