COQL Query in Events with What_Id and Join

COQL Query in Events with What_Id and Join

I'm trying to return fields in a lead related to an Event in Zoho CRM.  Looking a the documentation https://www.zoho.com/crm/developer/docs/api/v3/Get-Records-through-COQL-Query.html it says the format sample is {
    "select_query": "select 'What_Id->!Leads.Last_Name' from Tasks where 'What_Id->!Leads.id' = '4150868000004479013'"
}

Below are two identical queries other than adding the What_Id->Leads.First_Name field as a returned column.  Can anyone support with where I'm going wrong?

Successful Query

queryMap = Map();
queryMap.put("select_query","select What_Id from Events where Event_Title = Test");
info queryMap;
response = invokeurl
[
type :POST
parameters: queryMap.toString()
connection:"coql"
];
info response;

Returns Success and I can see the data


Failed Query
queryMap = Map();
queryMap.put("select_query","select What_Id, 'What_Id->!Leads.Last_Name' from Events where Event_Title = Test");
info queryMap;
response = invokeurl
[
type :POST
parameters: queryMap.toString()
connection:"coql"
];
info response;

Error:  
  • {"code":"INVALID_QUERY","details":{"column_name":"What_Id->!Leads.Last_Name"},"message":"column given seems to be invalid","status":"error"}