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