> ## Documentation Index > Fetch the complete documentation index at: https://docs.upflow.io/llms.txt > Use this file to discover all available pages before exploring further. # Upflow API - Data flows > Understand the main flows when integrating a billing system with Upflow — which entities like customers, invoices, payments, and credit notes to import. Here are the main flows to consider if you are building a full integration between your billing/accounting system and Upflow. The diagram includes the entities to import and the endpoints to use. Diagram of the Upflow API integration data flows: which entities (customers, invoices, payments, credit notes) to import via which endpoints