If you looking to use REST API version of our app. You can follow same procedure to run as firebase.
Once app will launch you can create account or login and order item. All the functionality will work as expected.
You can go to providers > const.service.ts
You can see api pointing to NodeJS backend. If you have own Backend you can replace this url with your own URL or if you like to get our backend you can purchase and host it on your own server. You can go to our product page to check API Details and there pricing.
NodeJS API Details Check out the details of NodeJS api backend . We use MongoDB as database for this backend .