I would guess that the App will work over the Internet, but it isn’t really for Customer use, since you need to buy a license for every Device that you install it on.
The App is based on a GraphQL Engine and SignalR Server inside SambaPOS Messaging Service.
PMPOS and Gloria Food integration utilize GraphQL…
https://forum.sambapos.com/t/integrators-graphql-api-guide/14047
GQL Modules also employs GraphQL and a connection to SignalR. But again, it is not intended for Customer use.
If you want to build your own Online Ordering system, you need to learn HTML, CSS, and Javascript, Then you use GraphQL Queries and Mutations to send and retrieve data to/from the SambaPOS Server, via AJAX (likely via the JQuery library)…
Study the Integrators Guide, study the PMPOS on GitHub, study GQL Modules. They all use similar mechanisms.