This feature is currently in beta.
Create 'Facebook for Developers' account here:
https://developers.facebook.com/docs/development/register
Create an app by following this guide:
https://developers.facebook.com/docs/development/create-an-app
In step 2 (choose an app type) choose Manage Business Integrations:
You will be directed into dashboard after the account creation.
Go to 'Settings > Basic' and add your domain (with 'http', 'https' and without protocol):
Access token generation in Events Manager:
Go to Events Manager, choose your Pixel and go to settings. Scroll down to Conversions API and click 'Generate access token':
Paste your Access Token here: