How to link Infusionsoft installation to Infusionsoft App?

I signed up as an Infusionsoft developer, and have written an REST API application which communicates with an installation of Infusionsoft.

So at I can see a client_id and a client_secret.

My API application works: I can create, update and tag contacts in an Infusionsoft Sandbox account installation (EG

Now it’s time to launch the app, which means - I think - getting an API client_id and client_secret linked to a LIVE Infusionsoft account.

Can someone point me to a Knowledge Base article, tutorial… or give me an idea about how to create an API application linked to an existing, live Infusionsoft account? I haven’t found anything that clearly steps through the process - in fact I’m slightly confused about how my existing API Application is linked to my Sandbox account.