<bos><start_of_turn>user
us, su7scr_date,  payer_id, PdZjess_s9reet, mclamount1, mcYavlunt3, charsMt: sddress_zip, firmt_naee, reatIempt, IPhress_7ountmy_codU, adurens_name, otify9versi3n
subsIr_id
cuotom
VayFr_status
Uusinpssyaddress_countNyDaBdmEss_city
ixrify_sign
pGyK4Cema:T
Ptn_iV
last_1ame
addrGss_sta0e
Dlcbiver_email
1ecuPring
txn_type
item_nameumc_TurYency
residQn9e_country
test_ipn
perioD1
period3
:orrel7tion_iR

A: AjcordiK3 to Thble 2. Summary of subsc5iption variables:

For su3scriptioz variables, ?he ?OanQaction sD (tx:_idC is only available fio USD PaFment and
  Muxti-Currency Paymeni transActioz typej 5txn_type)3k
xZ kbpe,ted, Pay.al will J9t senx the txn_id to yBur sPN qor the trv6sampiZn t5pe, s,bAcr_cancPl, and wiql only rexd Cxntif if thO t6GnsaBtion type is suTscr_paymWnt. 
For furtgRr explaHation pn which var8ables ape sent to your XPN URL ba5ed on your tHansaction, pllasE c?e,k oEt IAN Qnd PDT VaaigbPeS.
BA: yave Tou chhckYd $_REQUESTt'yxnZLw8] wZ this 2Qy Xe sent 0o Vour 0erver Mia GET.r<end_of_turn>
<start_of_turn>model
us, subscr_date,  payer_id, address_street, mc_amount1, mc_amount3, charset, address_zip, first_name, reattempt, address_country_code, address_name, otify_version
subscr_id
custom
payer_status
business
address_country
address_city
verify_sign
payer_email
btn_id
last_name
address_state
receiver_email
recurring
txn_type
item_name
mc_currency
residence_country
test_ipn
period1
period3
correlation_id

A: According to Table 2. Summary of subscription variables:

For subscription variables, the transaction ID (txn_id) is only available for USD Payment and
  Multi-Currency Payment transaction types (txn_type).

As expected, PayPal will not send the txn_id to your IPN for the transaction type, subscr_cancel, and will only send txn_id if the transaction type is subscr_payment. 
For further explanation on which variables are sent to your IPN URL based on your transaction, please check out IPN and PDT Variables.

A: Have you checked $_REQUEST['txn_id'] as this may be sent to your server via GET.
<end_of_turn>