When processing an order, you might come across the "21100491 Product is invalid. Shipping error" error.
This happens when the Service Code chosen is not available for the account which is being used to process the order.
Feel free to follow the step-by-step guide written below or the video guide, as you prefer:
To solve this issue you will have to:
1. Choose a Service Level which is available for your account from the Default Service Code dropdown on the Import Orders screen
2. Press Save to apply the change to the batch
3. Process or Print and Process the order