The follow-up material has base unit of measure &

What causes this issue?

You have specified a follow-up material whose base unit of measure is
not identical to the base unit of measure of the discontinued material.

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?

Enter an allowed follow-up material or change the base units of measure
of the two materials so that they are identical.

Error message extract from SAP system. Copyright SAP SE.