Check digit for EAN & cannot be determined

What causes this issue?

The system could not determine the check digit for one of the following
reasons:
The EAN is blank or is made up only of zeros.
The EAN has more than 17 characters.
The EAN is alphanumeric.
The EAN category is blank.
You did not enter the normal check algorithm in Customizing for the EAN
category specified.

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?

Error message extract from SAP system. Copyright SAP SE.