50 AMP circuit breaker

Have you tested the 50 amp circuit for 120v at the power pole?

Have you tested the shore power cord for 120v at the coach end when plugged to the pole?

Have you measured for 120v at the inbound terminals to the breaker?

Are all the breakers on your inverter reset?

Yes, portion of the interior can go bad and the handle remain in the on position.
You can reset many by turning off all branch breakers then turn off main breaker applying light pressure toward off. Then turn the main breaker on, then each branch breaker one at a time.
Another item that could be suspect is the transfer switch. Verify that you have in deed lost incoming power to the main breaker by using a voltmeter. Turn off main and read each leg and across main breaker. Each leg to ground and neutral should read 120 volts plus or minus a couple volts. If shore power is correctly wired you should read 240 between the two legs.

Yes but first try flipping it on/off ten times. If this gets it to work, it still needs to be replaced.

Yes. Replaced one last year on the pedestal where we were camp hosting.