Note: Your account has to be activated before you can go live
See here for a guide to testing your app in sandbox mode.
Once you're done with testing you can switch to live mode by going back to the App you created and clicking on it. This will bring up the app overview.
Then, on the app overview, toggle the Live Mode switch to on and your app will be set to live.
Note: This will change your keys from test to live so ensure you update the public key in your widget implementation and secret key across your Mono API calls.
You can also watch this short video to follow the steps.