Getting Related Lists for Custom Modules

Getting Related Lists for Custom Modules

I have a custom module (CustomModule1) 'Presentations'. All of my 'Leads' have a lookup field that allows them to be tied to a given 'Presentation'. So the items from the 'Leads' module populate a related list 'Attendees' in the 'Presentations' module.

I'm trying to make an API call to get a list of 'Attendees' for a given 'Presentation' ID, and I'm struggling. To the best of my knolwedge the call should look like the one below:
  1. https://crm.zoho.com/crm/private/xml/Leads/getRelatedRecords?authtoken=<authtoken>&scope=crmapi&id=<PresentationID>&parentModule=CustomModule1
Am I missing something, or is there a limitation with getRelatedRecords and custom modules?

  1. <response   uri =" /crm/private/xml/Attendees/getRelatedRecords " >
    <error>
    <code> 4401 </code>
    <message>
    Unable to populate data, please check if mandatory value is entered correctly.
    </message>
    </error>
    </response>
Above is the response I get from the server. According to documentation, the only mandatory values are 
  1. authtoken
  2. scope
  3. id
  4. parentModule
All of which I've included in the above API call. Any insight?