When AOR of HR is missing in resignation approval still the transaction got approved

An employee submitted his resignation. But somehow the AOR was not assigned to his HR. and the resignation approval should go to line manager→ Reviewer→ HR.

But still the transaction got approved after reviewer approval.

In this case transaction should failed or throw an error as AOR is not assigned to respective HR.

What should be the solution so that transaction should failed or throw an error?