Automatic reservation is no valid reference

What causes this issue?

The reservation that you entered is an automatic reservation. It cannot
be used as a model for a manual reservation because it is linked with
a reference document (an order, for example).

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?

INCLUDE NA_EINGABE_PRUEFEN

Error message extract from SAP system. Copyright SAP SE.