Chargify is a subscription billing software service that offers a recurring billing and subscription management space.
Log into the Chargify app and open your dashboard. From the sidebar menu, under Config, click on Integrations. You will then be able to create a new API key, which you will paste in the Tray authentication window. You also need to provide your site name. For instance if your Chargify site URL is "https://trayio.chargify.com" you will enter "trayio".