On the My Apps & Credentials page, click Live or Sandbox depending on whether you need an app for testing (Sandbox) or going live (Live)
Click Create App under REST API apps. Any previously created REST API apps will appear in the table above the Create App button.
Enter the name of your REST API app in the App Name field, and select a Sandbox business account to associate with your app. Note: Remember that you can’t use a Live credit card in Sandbox, and you can’t use a test credit card in your Live account.
Click Create App. Your credentials, the client ID and secret, are displayed on the app details page that displays after you click Create App.
When you are ready to take your code live, make sure you create a Live app to get live credentials.