to start npm install npm run build npm start

Postman

1.Endpoint
    method: Get,  url: http://localhost:3000/api/items 
    Params: {app_id: '730', currency: 'EUR', tradable: true } //option

2.Endpoint
    method: Post, url:http://localhost:3000/api/purchase
    Body {x-www-form-urlencoded}: {
        username: 'user1', itemPrice: xx
    }