How to assign an item number to Smart form in Purchasing Requisition?

Summary: How to assign an item number to Smart form in Purchasing Requisition?

Content (please ensure you mask any confidential information): Due to business requirement that all item in the PO requires a item number so how to assign an item number to Smart Form in Purchasing Requisition?

My idea is, a fixed item number will be assigned to the Smart From according to the item's belonging item category

Version (include the version you are using, if applicable): 23D

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