No label in trade in box

When you initiated your trade-in, you should have received confirmation via email. Contact details for Apple, concerning your purchase/trade-in, should be included in this communication. Contact Apple for advice.

The shipping box may be sent to you in a plastic shipping envelope; be sure to check that all items are accounted for before discarding the outer wrapping. In some regions the shipping container will be mailed without an outer wrapping; in such instance, the return shipping label will be beneath the address label that was used to send the shipping box to you.

Try to peel off the label on the outside of the box

as there may be another already under that.

This is how it worked on the return box I received

last week.