Sounds like it may need to be charged? Try charging it with a USB cable. There have been some reports of camp speakers that don't charge in the dock, either because the battery is fully discharged or because there is a problem with the dock, but you should be able to charge it outside the car with a USB cable to see if you can get it to work properly.
And if you can't get it to work properly, call Rivian and they will fix it.