create table test_l_amounts
  (
    id number(2) primary key,
    amount number(15,3),
    expiry_date date,
    first_due_Date date
  );

insert all
  into TEST_L_AMOUNTS (id, amount, expiry_date,first_due_Date  ) values (1, 1000, to_date('01-01-2030','dd-mm-yyyy'), to_date('01-06-2021','dd-mm-yyyy'))
  into TEST_L_AMOUNTS (id, amount, expiry_date,first_due_Date  ) values (2, 750, to_date('01-01-2023','dd-mm-yyyy'), to_date('01-01-2022','dd-mm-yyyy'))
  into TEST_L_AMOUNTS (id, amount, expiry_date,first_due_Date  ) values (3, 500, to_date('01-05-2023','dd-mm-yyyy'), to_date('01-05-2021','dd-mm-yyyy'))
select * from dual;

           SELECT DTA.ID, row_number() over (partition by ID ORDER BY NULL) INS_NUMBER, 
                  AMOUNT/NUM_INSTALLMENTS INST_AMOUNT,
                  ADD_MONTHS(DTA.FIRST_DUE_DATE, (row_number() over (partition by ID ORDER BY NULL) -1)*6) INST_DUE_DATE
              FROM (
                      SELECT ID, AMOUNT, EXPIRY_DATE, FIRST_DUE_DATE, FLOOR(MONTHS_BETWEEN(EXPIRY_DATE, FIRST_DUE_DATE) /6) + 1 INST_MONTHS,
                             CASE WHEN (FLOOR(MONTHS_BETWEEN(EXPIRY_DATE, FIRST_DUE_DATE) /6) + 1) > 10
                              THEN 10
                              ELSE (FLOOR(MONTHS_BETWEEN(EXPIRY_DATE, FIRST_DUE_DATE) /6) + 1) 
                             END NUM_INSTALLMENTS
                        FROM TEST_L_AMOUNTS
                    ) DTA,
                    LATERAL (SELECT 1 FROM DUAL CONNECT BY LEVEL <= NUM_INSTALLMENTS);