You have a server with data from your POS to be integrated with srv4pos.com where your server gets articles/sales from srv4pos.com.

To fetch latest changes of taxes, categories, products and categories data use GET /modifications (getModifications()) . Keep providing seller version in from-to parameters to get historical information part-by-part. The idea is described in a very simple manner at Synchronization and Cashing article.

To fetch sales information from the server see Use Case #7. Sales analysis