we unpacked an arm and a lot of empty space

They sent a photo of a closed crate with our order number taped on. Nothing showing the contents or who collected it. Better than the same tracking screenshot again, just not much better.

A labelled crate is not proof of collection. Ask them to link its crate mark to the missing-item packing list and carrier acceptance.

Purchasing has sent that request. We also made the inventory clearer because the seller keeps asking whether the adapter was tucked in with the arm. We checked all of it.

Does the photographed crate have a readable shipping mark distinct from the order number? That may help link later dispatch evidence to this particular package.

And keep the distinction in your notes: photographed crate, contents unconfirmed, dispatch unconfirmed. Don't promote it to in transit because a label exists.

Did your forwarder receive a booking for a second package? They may be able to check the reference cheaply, even if they cannot confirm the seller has released it.

Worth asking. A booking still isn't collection, but it may give you another reference to chase instead of another photograph.

Any answer from the forwarder? Especially whether the second reference identifies your crate or only a planned booking.

Forwarder found a booking, cancelled before collection. Purchasing has that in writing now and is asking the seller for a new dispatch plan. Training is off the calendar. I'd rather rebook it than keep moving the same hopeful date.

That is something concrete to put back to them. Still missing equipment, still no confirmed replacement dispatch. Keep both outstanding items on the case.