Tracking links are unique URLs for your job's online application that can be pasted on an external job board and/or as part of the marketing of the job. When candidates apply through a tracking link, they will be tagged with a pre-determined Source and Credit.
At this time, tracking links do not work on Craigslist. This is due to the fact that Craigslist blocks all tracking links from Applicant Tracking Systems (ATS) like Greenhouse Recruiting to prevent spamming and abuse from organizations.
As an alternative workflow, you can create a custom application question such as: How did you hear about this job? and include Craigslist as an available option. Next, make the response required and post the URL to the job application on Craigslist.