For multiple currency orders, we may encounter this error when editing an order. If customer requests to change sizes or variants of an order and we received this error, here are the steps we have to follow.
Create new order draft with everything correct, send invoice to customer.
Verify customer's information
Make sure that the correct product variant is placed
Inform the customer that they will receive an invoice and they have to pay for it.
Advise to notify us via email or phone that the new order was paid for / processed.
Once we verify they paid for the 2nd one, we then refund the 1st one in full and cancel it entirely
What we don't want to do is just refund 100% and tell the customer to re-place their order. That takes a lot more effort/time on the customers hands' and a lot of times they just will not re-order anything.
If the customer declines or does not want to go through the process, then we can refund the initial order and have the customer re-order.