WelcomeTrack (http://www.welcometrack.com/) collects and analyzes real-time data from e-merchants, their logistics experts and carriers, and offers an innovative solution based on recognized expertise. The WelcomeTrack app helps you keep track of the orders for your client (matching using client's email)
Connect on WelcomeTrack with your account, click on the settings icon (top right menu) and choose 'Clé API' (API keys). Click on the 'Create' button', select a name for the key (i.e. Zendesk integration key) and click on 'Save'. Copy and paste the automatically generated key value and use it when you install the app in Zendesk from the marketplace.