The error (Order Number: Message: ShopifyConnector/CreateFulfillment -> Error Message: {"errors":{"line_items":"array contains unpermitted members"}}) from Shopify typically occurs due to a dropped connection during fulfillment or because the order has already been marked as fulfilled in Shopify.
To resolve this issue please review the steps below:
Check if the order is already marked as fulfilled in Shopify.
If not, it may be a connection issue that occurred during the fulfillment process.
Go to Connect then Import Errors in Mintsoft.
Tick the affected order, then from the Bulk Actions drop-down, select Resync Connect Action.
By following these steps, you should be able to resolve the error.