Generate contract invoice lines in a specific sequence

Summary:

Generate contract invoice lines in a specific sequence

Content (please ensure you mask any confidential information):

Is there any setup that can be done, to ensure lines of a contract invoice are generated only in the sequence of events that underlie the invoice lines.

eg: if there are three events e1 (created first),e2 (second) and e3 (created last).These events are billed in a single invoice.
E1 should generate line1 , e2 line 2 and e3 should generate line3.
This is not happening currently on our system.

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

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