Most likely you will need a new converter. I’d check connections at battery and make sure they are tight. New unit but stuff happens. I’m assuming g since it’s newnthe battery is hooked up properly. Go to any auto parts store and get right amperage fuse. Sounds like a thermal issue or sense issue with that converter.
You could also disconnect battery making sure to cover both leads. Then plug unit into shore power with proper amperage fuse installed and see if converter runs. Measure DC voltage and you should see around 13.4 to 13.8. If not fine your converter model number.... most likely a WFCO and use this trouble shooting tree
http://wfcoelectronics.com/wp-conten...800-Series.pdf