The only cause for seeing the message MissingEmptyFulfillment, is if there is already a tracking number saved on the fulfillment.
This can happen if:
- The order has already been sent
- You forgot to save/print the PDF label when it was returnered
- There occurred an error in returning the label, so the tracking was saved but the PDF label disappeared
To create a new label for the order you need to edit the current tracking number to 0, save the settings, then print a new label.
Step 1 - Edit tracking number
Step 2 - Edit to 0 (zero)
Step 3 - Generate new label