Enable the second ref field in Business Settings > Purchase Orders:
Switch this On.
Now switch on the counter and set a start number. In the above screen, 9000 will be our starting sequential number.
Next, decide when you want the number to be generated. The choice is “On Approval” or “On sent to supplier”
The purchase will need to go into an approval process for this to work. Make sure you have your workflows and default workflow set correctly and that the buyers cannot override this.
On sent to Supplier
For this to work you would ideally have a “send to supplier” workflow step or an approval process that sends an email to the originator telling them to send off the order. If the originator is sending the order manually, from within the order, they will need to click the send icon – the number will only be generated as part of this step or the workflow step.