The MVC is REQUIRED to accept your temporary boat safety certificate - see the law
Currently, you must make an appointment with the NJ Motor Vehicle Division to obtain the boat license endorsement on your driver's license:
NJ MVC | How to get a Motorboat or Jet Ski License (state.nj.us)
Go to the NJMVC "Cheat Sheet" : PowerPoint Presentation (state.nj.us)
Under "FIRST TIME LICENSE/ID" and next to "First time license/ID/permit" choose "Appointment Only"
On the Schedule Appointments Online page, select "MAKE APPOINTMENT"
On the "INITIAL PERMIT (NOT FOR KNOWLEDGE TEST) Select the appointment button
**You'll see the last option is "Purchase a boat license (ages 16+)"
From the Map, select the town you want to go to, and you'll see a calendar and available appointment times, follow the prompts