There can be cases where a buyer orders a large number of items, and you can not ship them all in one shipment. So you need to separate them out over multiple shipments, requiring you to add multiple tracking numbers to the order. Here is how to handle that in LM.
Note, this applies to FBM orders, NOT FBA.
Add the first tracking number to the order. Since the tracking number will not have the full QTY of the order, LM will allow you to add another tracking number.
Then you can add the second tracking number.
Add as many tracking numbers as you need to reach the full QTY of the order. Once ALL QTY has been accounted for, LM will notify the marketplace that the order has been shipped!
And that is all there is to it!