The best way to integrate with Zapier is actually directly through your Stripe account.
Connect Zapier via Stripe settings response.
If you connected your own Stripe account via our “settings” tab after starting your trial: When a member pays it can trigger anything you want through Stripe's Zapier app.
If you go that route there is no need to use our API key, as it's a direct connection between your Stripe and Zapier.