All capacity reqmts for planned order will be deleted, as routing deleted

What causes this issue?

The system deletes all capacity requirements for the planned order to
be reduced as the corresponding routing has been deleted since the
planned order was created.

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?

Error message extract from SAP system. Copyright SAP SE.