How to populate field value from transaction header to transaction line by customization

Summary: When business users manually enter the PO Number field value at Transaction Header in Receivables->Billing, all the transaction lines PO Number DFF field should get automatically populated with the same PO Number through any customization approach.

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

24B

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

Screenshot of PO Number at Transaction Header:

Screenshot of PO Number at Transaction Line: