How to restrict user from entering duplicate Invoice_Number in an invoice?

Summary:

When user put Invoice_number inside the invoice it should restrict the user when clicks on Finished if that invoice_number is already present for other invoices

Can someone please help me on this how to achieve this?

Content (please ensure you mask any confidential information):

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

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