Create an account on developer.infusionsoft.com.
Login to the developer account.
Click Get Started.
Scroll down and click OAuth Guide under OAuth 2.0 Step 2.
Under Step 3 click Request Permission.
Copy and paste this link in a new tab. "https://signin.infusionsoft.com/app/oauth/authorize/client_id=(paste in the client ID which you have received on developer accounts page)".
Ensure that the you are logged in to the application.
You will be taken to your Account central.
Click API Access.