It doesn't. But does the order actually distinguish an installed adapter from a spare? Put that line beside the delivered contents. A photo can prove one is fitted without saying anything about whether two were ordered.
Then ask them to account for the second item specifically. They may be answering the wrong question because the message subject says missing adapter and the person replying sees one on the robot.
Was the spare meant to be loose in the robot crate, or in an accessory carton? That could direct the warehouse search, though it does not change the quantity.
Good question. Ask for their packing record for that specific item, rather than another general package photo. If they say it was sent separately, there should be a shipment they can identify.
Inventory mismatch. I would compare the spare list with every bag label before buying a replacement; actually, photograph the labels as well, because a wrong description can hide the right item. We found a mounting plate entered as a spacer once.
Did they find a packing entry, or are they still discussing the installed part? It would be useful to know whether the clearer wording got this to their warehouse team.
At least the quantity dispute is over. Get a definite answer about separate dispatch before this becomes a promise attached to an order you'll never place. Admitting the omission and sending the part are still two jobs.