To add an extra surcharge to an order at checkout:
If you select the pre-defined adjustment, the total price will increase based on the amount specified in the Back Office. To add a pre-defined adjustment, see here.
Custom Surcharge allows you to declare your adjustment amount before the order can be completed.
Next, on the Order Surcharge modal, select either '%' or '$', enter your desired surcharge amount, then click Apply Changes to proceed.
After that, the order will get completed with the specified surcharge
No Surcharges means no adjustments will be applied and the order will get completed with its original total.