External batch number assignment: Enter a batch number

What causes this issue?

You create a production order with reference to a sales order item and
for a material that requires a parameter variant. However, a parameter
variant that can be used when the production order is created has not
been entered in the sales order item. Therefore, the production order
is created without a parameter variant. This has the following
consequences:
All change numbers with parameter effectivity are ignored when the
order is created. The corresponding changes are therefore not adopted
in the production order.
You cannot predefine particular change numbers as being applicable or
non-applicable for the creation of the order (direct assignment).

How to fix this error?

If you want to create the production order with a particular parameter
variant, first, maintain this parameter variant in the sales order item
and then create the production order.

Error message extract from SAP system. Copyright SAP SE.