User are recommended to process the orders only from SelluSeller and the order status will gets updated from SelluSeller to Marketplaces automatically.
If the order are processed directly on the seller center or Marketplace, the status will not be able to update accordingly and remain under packing stages.
To fix this, kindly engage our customer care team (help@selluseller.com) to assist on the order status (Completed) update.
Anchanto Support