Sales order does not allow make-to-order production

What causes this issue?

The sales order entered is not to be included in make-to-order
production.

System Response

Account assignment can only be carried out with sales orders created
with a requirements type for make-to-order production.

How to fix this error?

Enter a sales order that is to be included in make-to-order production.

Error message extract from SAP system. Copyright SAP SE.