How to get a list of Team Folders associated to a Project from the API?

How to get a list of Team Folders associated to a Project from the API?

I've tried the below, based on another article and was unsuccessful. 

  2. response = invokeurl
  3. [
  4. url :"https://projectsapi.zoho.com/api/v3/portal/" + _portalID + "/projects/" + _projectResID + "/folders"
  5. type :GET
  6. connection:"zohoprojects"
  7. ];
  8. info response;
I get this error: (I edited out the ID's)
{ status_code: '500' , method: 'GET' , instance: '/api/v3/portal/[_portalID ]/projects/[_projectResID ]/folders' , title: 'INTERNAL_SERVER_ERROR' , error_type: 'OPERATIONAL_VALIDATION_ERROR' , details: array(1) }