The Round Robin booking setting allows users to select time slots without first choosing a Resource to book with. The time slots displayed will include a "Resource ID" in the availableTime object for you to include in the POST /appointments request.

The value for roundRobin should be 0, 1, or 2, resulting in:
0: No round robin
1: Random selection
2: Balanced selection

When using the "Balanced" option, roundRobin will attempt to evenly distribute bookings, within the Resources who are available.

Round Robin in the OnSched API

Using Round Robin in the OnSched API is done in two steps, first you must find the available time for the user to select, without specifying a Resource ID. In order to do this, you will include the "roundRobin" queryParameter in the GET /availability request. Upon its return you will see a "resourceId" property in each available time object. Once an available time is selected, you'll pass this Resource ID to POST /appointments in order to complete the booking.

Round Robin in OnSched.js

Using Round Robin in OnSched.js only requires two parameters.

First is the use of the "roundRobin" parameter in the availabilityParams of the Availability Element, this will for OnSched.js to find a random Resource ID to select during the available time selection. Second is setting the value of "resourceId" to zero, if the resourceId is unspecified, all available times for every resource will be returned (i.e. you will expect duplicates of each time slot).