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Apple ($AAPL) is experiencing a rare thing for the brand: consumer apathy about its flagship product, the iPhone. In a rare move, Apple has begun discounting various iPhone models in order to bring sales up to a place that meets expectations.

The iPhone XS, Apple's top-of-the-line iPhone that succeeded the successful 10th-anniversary iPhone X, is getting its own slew of promotions in the form of trade-ins as sales aren't up to par either.

If Best Buy sales rank data tells us anything (and it does: Best Buy is the largest retailer of iPhones outside of Apple itself), the iPhone XS is indeed slumping.

iPhone XS

For all models of the iPhone XS, sales rank peaked in the fall after release, but it's seen a steady decline since, with a steep drop in early December, largely due to a precipitous drop in interest in the 512GB version of the phone.

The 64GB iteration of the iPhone XS saw the highest sales ranks and least steep dropoff, peaking at 2,690 for all Best Buy products in October. It rests this week at around 7,450.

The 256GB version of the XS saw its best day on October 4 when it hit rank 3,650 at Best Buy. Things haven't been so good for this phone since then, and it currently sits around 10,000.

The 512GB version of the iPhone XS had the worst showing of all the XS versions. The highest rank it saw was 17,100 out of all products sold at Best Buy. December has been even worse to the big-memory phone, and it's now seeing a sales rank of around 38,000.

iPhone XS Max

The iPhone XS Max, touted as having the largest display ever on an iPhone, had a better go out of the gate than its smaller XS sibling. On average, the XS Max peaked at rank # 3,450 on October 4. But, as the story seems to go for the XS, it's slowed down, currently sitting at an average rank of 9,370 across all XS Max models.

The best-selling version of the XS Max at Best Buy, the 64GB XS Max hit a top rank of 1,420 on October 4. It's since settled at 5,690.

The 256GB versio nof the XS Max peaked at 1,540 on October 4. it's not at around 6,630 as we head into the holidays.

The grand-daddy of all iPhone, the XS Max with 512GB of onboard memory, hit its peak of 7,380 on October 4. Time hasn't been kind to this model, either, however, and it now is ranked #15,800 at Best Buy.