Serialization with material &1 only possible after saving equipment

What causes this issue?

In the material master &V1&, equipment- and serial numbers should be
assigned synchronously, or to be precise: If the equipment number has
already been assigned, then the serial number must have the same value.

System Response

If the equipment number has not been assigned, then a serialization of
the equipment with material &V1& is not possible.

How to fix this error?

Save the equipment without a serial number and perform the
serialization subsequently in the change mode.
When creating serialized equipment (with material &V1&) in the future,
you should choose one of the following options:
Create the equipment with template material &V1& or
Create the equipment from the first as a serial number (for example,
using transaction IQ01) for material &V1&
In both cases the system automatically performs an "early" assignment
of the equipment number. That is, in both cases, serialization is
possible as soon as the master record is created.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.