How to avoid entry of duplicate external document number in sales order

Hi Users,

Is there any NAV standard out of box functionality or configuration which flags when an external document number is entered during the sales order process (this is typically the customer PO number). Whether the sales order entry person at the time of order choose to accept it and go ahead entering the duplicate?

No checking of uniqueness in standard, but it is easily achievable by small modification.

Actually, it’s a common request from endusers and thus widely implemented - I would say almost in 100% of projects where I have participated.

Practice shows it’s better to implement a warning system rather than complete blocking of duplicates - there are cases, when duplicates should be still allowed. Example - to correct entry errors in posted docs you need to make a CreditNote and additional correct Invoice, all with the same ExtDocNo.