If you are using a third-party plugin that customizes WooCommerce order numbers, whether it be random generated characters or having a prefix or suffix added to the order ID, this customized order number will also show in FooSales.
FooSales uses the WooCommerce get_order_number() function to get the customized order number. If you are not using a third-party plugin that customizes the order number, the default order ID will be shown. The customized order number is used for display purposes only, and can be seen on the Orders screen and printed receipts. You can also search for orders using the customized order number.