Serial number for material &1 must be the same as equipment number (&2)

What causes this issue?

In the material master &V1&, the equipment- and serial number 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 serial number should be maintained, then it should
only have the value &V2&.

How to fix this error?

Check if the serialization of the equipment should actually be
performed in the form which you have specified.
If this is the case, that is, a different assignment of equipment- and
serial numbers is really intended, then you should change the setting
in the material master record if necessary.

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.