Hello,
I wanted to share this setting since it took me a while to find it and searching the forums did not help.
With Ecommerce some marketplaces like Home Depot and Lowes will use the same customer order number. Normally having the Sales Order not allow duplicates is the correct setting but if enabled you will get orders that will not import since the Customer Order Nbr is the same.
Here is the screen name you need to navigate to change the setting.
Order Types (SO201000) > Choose SO as Order Type > Order Settings.