The job board feeds do not support job fair postings. Posting a job that references a "Job Fair" or "Hiring Fair" and includes multiple positions within the description to advertise your event will have lower visibility, if any at all.
We recommend separate job postings for each job for which you are hiring. You can use the Invite to Job feature to reach out to people you meet at your job fair and you can add a Tracking Link or Text to Apply to encourage applicants to apply.