InfoAll new integrations should use our latest API version — v5.
New features will be introduced exclusively in v5 version.
API v3 remains in support mode and will not receive further updates.
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 brand account to your store before moving forward with Backend integration.