Ultimately, hosts will need to display registration numbers on their listings. New York City has received 3,829 registration applications, reviewed 896 applications, and granted 290 as of Monday, according to Christian Klossner, executive director of the Mayor’s Office of Special Enforcement, which oversees the registration process. The office has denied 90 and returned another 516 seeking corrections or more information.

Airbnb says it began blocking new short-term reservations for unregistered rentals as early as August 14, but did not automatically cancel stays in unregistered apartments before December 1 to avoid disrupting guests’ travel plans. Expedia Group, the parent company of Vrbo, is working with “the city and our partners to meet the law’s requirements and minimize disruption to the city’s travelers and tourism economy,” says Richard de Sam Lazaro, the company’s senior director of government and corporate affairs. Booking.com did not respond to a request for comment.

But amid the chaotic rollout of the new law, a number of listings appear to be falling through the cracks. A search on Airbnb for apartments in New York for more than two guests returns several results that may break the new law. Entire homes are still available for booking, some with enough space for 12 or 14 guests. One, a townhouse in Harlem, has a backyard with a firepit, a living room with a pool table, and five bedrooms, some with multiple beds next to each other, set up hotel-style. It’s listed for around $1,400 per night.

Some of the listings still available may still be allowed on Airbnb. The new rule allows for hotels to list rooms on booking platforms and to continue to accept guests without having to register with the city. It was not immediately clear if some of the listings still on Airbnb qualify for this exemption. Airbnb did not comment on potentially illegal listings on its platform flagged by WIRED or on the data provided by Inside Airbnb.

Airbnb has fought against the New York City regulations, saying the change would seriously hamper both its business and host income in the city. To register, short-term rental hosts, whether on Airbnb, Vrbo, or elsewhere, must meet a strict set of conditions: They cannot rent out entire apartments, the host must be living in the home and be present during the booking, and only two guests can stay at a time. Hosts and platforms that facilitate illegal bookings could be penalized, but guests would not be.

Small landlords say the law unfairly targets people who try to list their own homes for rent while out of town, and smaller landlords who want to occasionally rent one apartment on a short-term basis. Whether or not the move to regulate short-term rentals in New York works has huge implications for other major tourist cities where the popularity of short-term rentals has contributed to housing shortages and affordability issues. And this initial hiccup shows how complicated it can be to get booking platforms and cities to talk to each other, while also having thousands of hosts apply to register their homes.