Your API key will be generated after you have an active paid plan inside ROI PANEL.
Without an active plan you will not be able to see it.
To access it you'll need to go to the profile settings tab which will become available on the top right hand side corner of your screen once you have an active plan.
And the API key will be displayed immediately below your member # (above the settings box)
So first select a plan and complete the checkout process and then you'll be able to access this immediately.