React redux async action error

I am pretty new to react and am having problems dispatching actions after API calls. I am not currently using any middleware that handles async actions. I was able to implement login, logout, and signup doing async api calls. I tried to implement an api call that gets all users and now I am getting this error. My getProfile() function is working perfectly with out any problems. My getUsers() function is throwing the error.

Error: Actions must be plain objects. Use custom middleware for async actions.

here are my actions

function profileRecieved(user){
  return {
    type: PROFILE_RECIEVED,
    user
  }
}

function usersRecieved(users){
  type: USERS_RECIEVED,
  users
}

export function getProfile(id){
  WebApi.get('/user/'+id, result => {
    if(result.status !== 200){
      console.log("ERROR");
    } else {
      store.dispatch(profileRecieved(result.data));
    }
  })
}

export function getUsers(){
  WebApi.get('/users', result => {
    store.dispatch(usersRecieved(result.data.users));
  })
}

here is my reducer

const initialState = {
  profileUser:{
    username: "",
    id:"",
    email: ""
  },
  users: []
};

const UserReducer = (state = initialState, action) => {
  switch(action.type) {
    case PROFILE_RECIEVED:
      return Object.assign({}, state, {
        profileUser: action.user
      });
    case USERS_RECIEVED:
      return Object.assign({}, state, {
        users : action.users
      });
    default:
      return state;
  }

and here is my WebApi class

var instance = axios.create({
  baseURL: BASE_URL,
  headers: {
    Authorization: localStorage.getItem("access_token")
  }
});

// All requests made with this class will have
// the Authorization header added to it
class WebApi{

  static get(route, callback){

    instance.get(route)
      .then(response => {
        callback(response);
      })
      .catch(err => {
        console.log(err);
      });
  }

   static post(route, data, callback){
    instance.post(route, data)
    .then(response => {
      callback(response);
    })
    .catch(err => {
      console.log(err);
    });
  }
}