FRM-40508: ORACLE error:unable to INSERT record

CREATE OR REPLACE PACKAGE schedule_checker
IS
  PROCEDURE lesson_checker(fk_ins_id  IN VARCHAR2,date_of  IN VARCHAR2);
  
  PROCEDURE time_check(TIME  IN NUMBER,class_she_id_vd  IN VARCHAR2);
END;

/
 
CREATE OR REPLACE PACKAGE BODY schedule_checker
IS
  PROCEDURE lesson_checker
       (fk_ins_id  IN VARCHAR2,
        date_of    IN VARCHAR2)
  IS
    total      NUMBER;
    ins_id_t   instructor.ins_id%TYPE;
    date_of_t  class_schedule.date_of%TYPE;
    CURSOR ins_count IS 
      SELECT   fk_ins_id,
               date_of,
               Count(*)
      FROM     class_schedule
      GROUP BY fk_ins_id,
               date_of;
  BEGIN
    OPEN ins_count;
    
    LOOP
      FETCH ins_count INTO ins_id_t,
      date_of_t,
      total;
      
      EXIT WHEN ins_count%NOTFOUND;
      
      IF (total >= 5) THEN
        Raise_application_error( - 20801,
                                'Instructor: ' || fk_ins_id || ' can not be assigned to more than 5 lessons on: ' || date_of_t);
      END IF;
    END LOOP;
    
    CLOSE ins_count;
  END lesson_checker;
  
  PROCEDURE time_check
       (TIME             IN NUMBER,
        class_she_id_vd  IN VARCHAR2)
  IS
  BEGIN
    IF (TIME NOT BETWEEN 09.00
                         AND 22.00) THEN
      Raise_application_error( - 20801,
                              ' Lesson can not be scheduled outside of Gym hours! ');
    END IF;
  END time_check;
END;

/

CREATE OR REPLACE TRIGGER class_schedule_trig
BEFORE INSERT OR UPDATE ON class_schedule
FOR EACH ROW
BEGIN

IF INSERTING THEN
schedule_checker.time_check(:new.time, :new.class_she_id);

END IF;

IF INSERTING THEN
schedule_checker.lesson_checker(:new.fk_ins_id, :new.date_of);
END IF;


IF UPDATING THEN
schedule_checker.time_check(:new.time, :new.class_she_id);

END IF;

IF UPDATING THEN
schedule_checker.lesson_checker(:new.fk_ins_id, :new.date_of);
END IF;

END;
/