Converter/Charger or Inverter/Converter/Charger
Here is a possible troubleshooting path for a converter/charger.
If you have an inverter/charger/converter, there is a whole different set of possibilities.
Plug into shore power. Test that 115 volts is available in the TT by running a 115 volt appliance.
Disconnect the battery.
Do 12 volt appliances and lights work?
If "no", converter/charger is not working.
My 2018 Kodiak Cub has a WFCO 30 amp all in one converter/charger, service panel. All of these functions are in one plastic box mounted in a cabinet.
There is one circuit breaker dedicated to the WFCO converter/charger. You said it is working OK. I assume you turned it off and back on again to reset it.
There are two fuses in the fuse panel that could interrupt charging. A 30 amp main and a 40 amp reverse polarity fuse. Either of them could shut down battery charging. Continuity check is the definitive test for a fuse. Appearances can be deceiving.
You said 12 volt appliances and light work from battery so a battery disconnect switch or disconnected or loose battery wire are not the problem.
Failing these easy tests, a deep dive into the converter/charger is warranted.
Some TT's have a service panel separate from the converter/charger. The converter/charger is likely to be inside a cabinet near the service panel. The converter/charger may be in an electrical service bay. Fuses and breakers can be anywhere in the wiring system.
Dutchman Kodiak Cub KD176RD 2018
Nissan Pathfinder 2015