Step 1: Activate Developer Mode (from Settings)

Step 2: Use “CTRL + K + /” to look for the Sequence menu, and search for “sale.order” or “purchase.order”

Set the “Implementation” as “No gap”.

Extra tip: You can reset the “Next number” from this menu if needed.

You can repeat this configuration for the purchase order sequence.

From now, when importing the purchase/sale orders, there won't be any gaps in the sequence.