When I got a new iPhone, I sold my iPhone 12 Pro Max 64GB to BuybackBoss, as they offered $653 and that seemed reasonable and covered my payoff. Verizon had it unlocked, which surprised me- I thought it was going to take 60 days after I close the account. The website is super easy, they emailed a PDF of a shipping label with no charge to me and in less than a week I had the cash.
https://buybackboss.com/