When processing an order you might come across the "Missing or invalid default region" error.
This error happens when the ZIP code provided in the order is incorrect.
Feel free to follow the step-by-step guide written below or the video guide, as you prefer:
To solve this issue you have to:
1. Edit the order from the Import Orders screen
2. Change the Postal code entered to a valid one according to the Address/City
3. Press Save to apply the changes
After doing so, if the rest of the information is correct, you should be able to Process or Process and Print correctly