NJ LLC doing business in NY
This is a question that cannot be definitively answered without the review of the particular facts by an attorney.
Generally speaking, in New York a company is subject to foreign registration when, among other factors, "the foreign corporation must do more than make a single contract, engage in an isolated piece of business, or an occasional undertaking; it must maintain and carry on business with some continuity of act and purpose." And, "the local or intrastate contacts with New York must be permanent, continuous, and regular."
I hope that answer gives you a clearer picture. If you have any further questions feel free to contact my office at your convenience.