The error message MissingShippingMethod will only be showed if there is no Smart Send data saved on an order to determine which label to generate.
There are 2 reason for this message to show.
- The order was placed on your shop before you installed and configured the Smart Send app. The order therefor has no Smart Send data present to create the label.
In this case you will have to either add a Shopify backend shipping method or create the label manually.
- The shipping rate chosen on the order has not been matched with a shipping method in the Smart Send app in the tab Shipping methods.
When you have assigned all Shopify freight rates a Shipping method in the Smart Send app, try placing a test order and create a label to it with the method that previously failed. If you succeed with the label, the label creation will work on all future orders. For the current order that fails, you will have to create the label manually with your carrier.