ScoZone Said:
"Didn't receive trade-in box: I ordered a new iPhone XR, setting up a trade-in of my iPhone 7. The information on the website and email said that I would receive a box in which to return my old phone. I had the new iPhone delivered by courier[...] but I did not receive the return box. Is the box coming separately, or... how do I send my iPhone 7 back so I can get my trade-in refund?"
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About the Trade-In Box:
The box comes separately. It has its own box in it, made for proper packaging. So, essentially, it is a box-within-a-box. You send it back in it. The box to send in has all the paperwork and stickers for you to use.
Call Apple Support:
If anything were to get in the way, or if you are in an extreme a rural area, it would make sense for it all to be behind schedule, perhaps. But contact Apple Support, informing them that you have not yet received this box. Apple sends you an eMail so you can track this down. If someone is not there to pick it up, it may be back at the postal service awaiting your pickup. This is typical by Terms & Conditions.
Info on Contacting Apple: