Different attribution channels for revenue in Google Analytics
All the traffic in Google Analytics gets attributed to "Direct".
Develop the possibility to attribute revenue to different channels such as "Paid" and "Organic" or others.
Tracking of traffic sources is achievable by using different UTM parameters for different campaign or traffic source. In other words, if you want to distinguish between multiple sources of you traffic leading to the same landing page, you simply attach different UTM parameter).
Read about the principle of UTM parameters here: https://support.google.com/analytics/answer/1033863?hl=en.
The easiest is to generate the link for every campaign/source of traffic via UTM builder: https://ga-dev-tools.appspot.com/campaign-url-builder/
I hope that helps.