External applications
External applications work outside of Ecwid control panel and they also have an app details page for easy installation process. These apps use oAuth2 flow to get access token for a specific Ecwid store.
Check external apps guideline for general guides
The installation process starts with user visiting app details page. On that page, they can install the app by providing the necessary permissions to it. Once the user clicks the "Install" button, Ecwid sends a user to your app's Return URL along with the temporary code in the URL parameters.
Mind that in this case the installation process starts on Ecwid side and it might be the first time they open your site. Make sure your page on the return URL onboards users well – this is a landing page for them in your service. We recommend prefilling user details like: Name, email, Store name, Store ID and other fields that your service needs.
See External applications guideline for more information.