Yes, this integration works for both new and existing iZettle customers. Go to the Starling Marketplace, tap  on Browse, and select iZettle from the menu. Tap  Add and then select Login to iZettle. Follow the links, which will take you to log into your iZettle account. From there, you’ll be prompted to confirm you agree to sharing the required iZettle data with Starling. This video outlines the steps you need to take.  See video here