[Solved]-what is this error message for ? Actions must be plain objects. Use custom middleware for async actions-Reactjs

It seems that the code is currently broken, you can fix this issue by change:

const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION__ || compose;

const store = createStore(burgerBuilderReducer, composeEnhancers(
    applyMiddleware(thunk)
));

with:

const store = createStore(
  rootReducer,
  //composeEnhancers(applyMiddleware(thunk)) // => NOTE: This would break the code!
  // Thisone instead will work fine...
  compose(
    applyMiddleware(
      thunk
      // Other middlewares
    ),
    window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__() // Chrome debugger
  )
);