Backend API (server side) is a secure way to exchange information. It has all available functionality except popups and forms (you need to use Javascript snippet for them to work.). Please be sure you have already created and connected your Omnisend account to your store prior moving forward with Backend integration. If you have not done that yet, please read our Before you begin guide.
Endpoint
Current endpoint link: https://api.omnisend.com/v3/
You can find out API updates and upcoming updates in our Developer center