Contract Query: Drill down From Contract to AR Invoice

SELECT okh.contract_number,
   okh.start_date contract_start_date,
   okh.end_date contract_end_date,
   oksl.line_number Sub_line_number,
   okbc.bill_action,
   okbt.trx_number invoice_number,
   okbs.date_billed_from,
   okbs.date_billed_to,
  (SELECT a.segment1
   FROM mtl_system_items_b a,
     csi_item_instances b,
okc_k_items c
   WHERE a.inventory_item_id = b.inventory_item_id
     and c.dnz_chr_id = okh.id
     and c.jtot_object1_code = 'OKX_CUSTPROD'
     and b.instance_id = c.object1_id1
     and a.organization_id = b.inv_master_organization_id
     and c.cle_id = oksl.id) product_item,
  (SELECT b.serial_number
   FROM mtl_system_items_b a,
     csi_item_instances b,
okc_k_items c
   WHERE a.inventory_item_id = b.inventory_item_id
     and c.dnz_chr_id = okh.id
     and c.jtot_object1_code = 'OKX_CUSTPROD'
     and b.instance_id = c.object1_id1
     and a.organization_id = b.inv_master_organization_id
     and c.cle_id = oksl.id) serial_number
FROM okc_k_headers_all_b okh,
  okc_k_lines_b okl,
  okc_k_lines_b oksl,
  oks_bill_sub_lines okbs,
  oks_bill_txn_lines okbt,
  oks_bill_cont_lines okbc
WHERE okh.id = okl.chr_id
  AND okl.id = oksl.cle_id
  AND oksl.id = okbs.cle_id
  AND okbs.bcl_id = okbt.bcl_id
  AND okbt.bcl_id = okbc.id
--AND okbt.trx_number = '91107083'
  AND okh.contract_number = 'SMFR00069'
ORDER BY okbt.trx_number;