ORDS, SODA & JSON in the Database

I have a cursor that contains a cursor as in the example below:

DECLARE
  c sys_refcursor;
BEGIN
open c for select deptno,                    
                          dname,                     
                         cursor(select empno,                                  
                                                   ename                             
                                                    from emp e
                                                 where e.deptno=d.deptno) emps              
                from dept d;  
apex_json.open_object;   a
pex_json. write('departments', c);   
apex_json.close_object;

If I write this output to a clob it works fine.  If I remove the inner cursor it works fine over ORDS.

However with the inner cursor if I try to write it over ORDS...I get an indecipherable:

555 User Defined Resource Error
Does anyone have any ideas what might be happening here?

(Using autonomous database : Version 19c, ORDS: 19)