Approve subscription when ad-hoc bill lines are added

Summary:

How can we add an Approval hierarchy whenever ad-hoc bill lines are added to the subscription.

Content (please ensure you mask any confidential information):

We want to make the subscription undergo approval cycle whenever a new ad-hoc bill line gets added to it.

Is there a way to do this using BPM?

Version (include the version you are using, if applicable):

24D

Code Snippet (add any code snippets that support your topic, if applicable):