Error when deploying app on Heroku or Railway

Question

This is my first time deploying a MERN app and I keep coming across these errors:

I'm getting this error when attempting to deploy it in Heroku:

remote: Module not found: Error: Can't resolve './Store' in '/tmp/build_1d3d428a/frontend/src'

I wanted to try deploying it using another technology because I heard that Heroku was having issues. This error comes up when I try deploying the same app in Railway:

Failed to compile. Module not found: Error: Can't resolve './Store' in '/workspace/frontend/src'

I'm guessing something is wrong with the Store file but I'm not sure what it is. Here is the code in that file:

import { createContext, useReducer } from "react";

export const Store = createContext();

//define initial state in cart based on local storage
const initialState = {
  //check if user exists
  userInfo: localStorage.getItem("userInfo")
    ? JSON.parse(localStorage.getItem("userInfo"))
    : null,

  cart: {
    //get shipping address, payment method and cart items based on user
    shippingAddress: localStorage.getItem("shippingAddress")
      ? JSON.parse(localStorage.getItem("shippingAddress"))
      : {},
    paymentMethod: localStorage.getItem("paymentMethod")
      ? localStorage.getItem("paymentMethod")
      : "",
    cartItems: localStorage.getItem("cartItems")
      ? JSON.parse(localStorage.getItem("cartItems"))
      : [],
  },
};

//update state in cart
//instead of creating duplicate items of the same product, we increase the amount of the one product if button is pressed more than once

function reducer(state, action) {
  switch (action.type) {
    //add items to cart
    case "CART_ADD_ITEM":
      const newItem = action.payload;
      const existItem = state.cart.cartItems.find(
        (item) => item._id === newItem._id
      );
      const cartItems = existItem
        ? state.cart.cartItems.map((item) =>
            item._id === existItem._id ? newItem : item
          )
        : [...state.cart.cartItems, newItem];
      localStorage.setItem("cartItems", JSON.stringify(cartItems));
      return { ...state, cart: { ...state.cart, cartItems } };
    //second case: remove item from cart
    case "CART_REMOVE_ITEM": {
      const cartItems = state.cart.cartItems.filter(
        (item) => item._id !== action.payload._id
      );
      localStorage.setItem("cartItems", JSON.stringify(cartItems));
      return { ...state, cart: { ...state.cart, cartItems } };
    }
    //clear cart
    case "CART_CLEAR":
      return { ...state, cart: { ...state.cart, cartItems: [] } };
    //update user info based on data from the backend
    case "USER_SIGNIN":
      return { ...state, userInfo: action.payload };
    //case where user is signed out
    case "USER_SIGNOUT":
      return {
        ...state,
        userInfo: null,
        cart: {
          cartItems: [],
          shippingAddress: {},
          paymentMethod: "",
        },
      };
    //update shipping address with data from payload
    case "SAVE_SHIPPING_ADDRESS":
      return {
        ...state,
        cart: { ...state.cart, shippingAddress: action.payload },
      };
    //save payment method
    case "SAVE_PAYMENT_METHOD":
      return {
        ...state,
        cart: { ...state.cart, paymentMethod: action.payload },
      };
    default:
      return state;
  }
}

export function StoreProvider(props) {
  const [state, dispatch] = useReducer(reducer, initialState);
  const value = { state, dispatch: dispatch };
  return <Store.Provider value={value}>{props.children}</Store.Provider>;
}

Please let me know if I should include anything else. I'm not sure what is making the file/app undeployable.