To find your API Parternize credentials you will have to do some actions.
1. Log in to your account, then click on Reporting > Performance:
2. Then click on the Download button:
3. Copy/past the first input (JSON API Link) and you will have something like this :
https://api_id:firstname.lastname@example.org/..., you will have to copy the api_id to Api user ID and api_key to API Key.
And connect your Performance Horizon to see your affiliate report !