it's the publishable key, that's the one meant to be used when creating integrations, also you should be able to get a test publishable key, though we only use the key to read products and prices
tedyoung the idea of the platform is that you already have a Stripe account with products and prices, the platform will allow you to put together a pricing widget in minutes to embed into you page. IF you're interested I can provide a test key for testing