Build a web application

I need a web app from where my users can publish their product details to multiple marketplace websites at the same posting instance. They will enter in their product details and this details will be published to other sites linked to our web app via API. They will also be able to manage their product postings on all those sites. I need a web app where my users can sign up to publish their products to about 5 different marketplace websites. For example, they'll post one product and that product will be published on 5 marketplace websites. These other websites are marketplace websites like [login to view URL] where a user can own a shop/store where they can post and manage their products. Users who have accounts with these marketplace websites will manage their account from our website. This means that our website will be linked to these marketplace websites via API which you'll build so that the users can successfully log in to add, remove, edit products they have posted on all these websites. They can also manage their orders and account settings on these websites. For every order they receive they'll be alerted via SMS. (This is like the [login to view URL] app where you can sign in to post on all your social accounts from one website) included in the websites are facebook; any product posted via the app will show up on their facebook page which they must have added to the app. User will approve(tick) the websites he wants for each post to be published to for every product he is adding. Also included is [login to view URL]