What this is
Available capacity sits at zero or near it, while the product continues to appear in catalogs with an attractive headline APR. In data terms, the remaining capacity reads as zero or as a cap-reached state. The trap is about whether the rate is transactable, not about whether the rate itself is misstated.
What it means for you
The headline APR is not actionable at the present time: any attempt to subscribe returns a capacity-reached response. The trap costs no money, only decision time: the expectation formed on the basis of this APR must be carried to a different product.
In practice
A CEX promotional product fronted on the catalog homepage at 9.5% APR while its available capacity has been exhausted (the cap-reached flag is set). The subscription button returns a "sold out" message. The APR on the front page is, at this moment, an unfillable quote.