The interval & is not internal

What causes this issue?

By specifying an EAN category, you have attempted to have the system
assign an EAN or UPC. However, as the internal interval, this EAN
category is assigned an interval that is either not defined or that is
defined as an external interval for the number range object.

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?

Ask your systems administrator to correct the error.

Error message extract from SAP system. Copyright SAP SE.