Purchasing organization & does not exist

What causes this issue?

The error analysis of the defective record found that a purchasing
organization does not exist.

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?

If you no longer need the assignment, delete the line.
Otherwise, create the purchasing organization and start the assignment
again.

Error message extract from SAP system. Copyright SAP SE.