Please check the destinations for parallel MRP

What causes this issue?

No destinations have been entered in Customizing or none of the the
destinations (application server) entered are active.
In Customizing for MRP, you define the logical destinations (servers)
to be used for parallel processing.

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.