JVZoo not modifying level0 member to level1 following purchase

I am setting up s2member for a client. They are using JVZoo with paypal to handle their payment processing and affiliate tracking.

When a level 0 user is logged in, they are shown a purchase button for an upgrade to level 1. This button takes them to JVZoo, then to paypal to complete payment.

After payment, the user is brought back to the website, but they are still listed as a subscriber. They receive an email giving them instructions to register a new account.

Somehow, it appears the modify=1 POST variable is getting lost in the process. Does anybody have any idea how I can include that?

Here the log output from the test transaction

LOG ENTRY: Thu Nov 19th, 2015 @ precisely 8:35 pm UTC
PHP v5.4.45 :: WordPress v4.3.1 :: s2Member v150925
Memory 28.61 MB :: Real Memory 28.75 MB :: Peak Memory 28.74 MB :: Real Peak Memory 29.00 MB
unlimited20.com/?s2member_paypal_notify=1
User-Agent: PayPal IPN ( https://www.paypal.com/ipn )
array (
‘mc_gross’ => ‘0.50’,
‘invoice’ => ‘Unlimited 20 System (1447965296)’,
‘protection_eligibility’ => ‘Ineligible’,
‘item_number1’ => ”,
‘payer_id’ => ‘GRYURTN9E6JDJ’,
‘tax’ => ‘0.00’,
‘payment_date’ => ’12:35:15 Nov 19, 2015 PST’,
‘payment_status’ => ‘Completed’,
‘charset’ => ‘windows-1252’,
‘mc_shipping’ => ‘0.00’,
‘mc_handling’ => ‘0.00’,
‘first_name’ => ‘Micah’,
‘mc_fee’ => ‘0.31’,
‘notify_version’ => ‘3.8’,
‘custom’ => ”,
‘payer_status’ => ‘verified’,
‘business’ => ‘ryanjmaynard21@gmail.com’,
‘num_cart_items’ => ‘1’,
‘mc_handling1’ => ‘0.00’,
‘verify_sign’ => ‘ASvutlzDO.h1qfue-hNHvkLB7eIeADfaEzpw2lESeb4XUyOGTswzJhhO’,
‘payer_email’ => ‘micah@micahfox.com’,
‘mc_shipping1’ => ‘0.00’,
‘tax1’ => ‘0.00’,
‘memo’ => ‘MTQ0Nzk2NTI5Ni0xODUyOTEtMC00NS4zNy4yNDUuMjQ0’,
‘txn_id’ => ‘9SE42806Y32450824’,
‘payment_type’ => ‘instant’,
‘last_name’ => ‘Fox’,
‘item_name1’ => ‘Unlimited 20 System’,
‘receiver_email’ => ‘ryanjmaynard21@gmail.com’,
‘payment_fee’ => ‘0.31’,
‘quantity1’ => ‘1’,
‘receiver_id’ => ‘KKEHHV6D3EB5U’,
‘txn_type’ => ‘cart’,
‘mc_gross_1’ => ‘0.50’,
‘mc_currency’ => ‘USD’,
‘residence_country’ => ‘US’,
‘transaction_subject’ => ”,
‘payment_gross’ => ‘0.50’,
‘ipn_track_id’ => ‘acaab65d297f0’,
‘s2member_log’ =>
array (
0 => ‘IPN received on: Thu Nov 19, 2015 8:35:24 pm UTC’,
1 => ‘s2Member POST vars verified through a POST back to PayPal.’,
2 => ‘Unable to verify $_SERVER["HTTP_HOST"]. Please check the custom value in your Button Code. It MUST start with your domain name.’,
),
‘subscr_gateway’ => ‘paypal’,
)

LOG ENTRY: Thu Nov 19th, 2015 @ precisely 8:35 pm UTC
PHP v5.4.45 :: WordPress v4.3.1 :: s2Member v150925
Memory 30.82 MB :: Real Memory 31.25 MB :: Peak Memory 31.18 MB :: Real Peak Memory 31.25 MB
unlimited20.com/?s2member_paypal_notify=1&s2member_paypal_proxy=JVzoo&modify=1&s2member_paypal_proxy_verification=fe376224669a201477d269df8e713d5b
User-Agent:
array (
‘modify’ => ‘1’,
‘business’ => ‘<removed>’,
‘charset’ => ‘windows-1252’,
‘custom’ => ‘<removed>’,
‘first_name’ => ‘Micah’,
‘invoice’ => ‘<removed>’,
‘ipn_track_id’ => ‘9G5554813M769074G’,
‘item_name1’ => ‘<removed>’,
‘item_number’ => ‘1’,
‘item_number1’ => ”,
‘last_name’ => ‘Fox’,
‘mc_currency’ => ‘USD’,
‘mc_fee’ => ‘0.01’,
‘mc_gross’ => ‘0.01’,
‘mc_gross_1’ => ‘0.01’,
‘mc_handling’ => ”,
‘mc_handling1’ => ‘0.00’,
‘mc_shipping’ => ‘0.00’,
‘mc_shipping1’ => ‘0.00’,
‘memo’ => ”,
‘notify_version’ => ‘3.4’,
‘num_cart_items’ => ‘1’,
‘payer_business_name’ => ‘Micah Fox’,
‘payer_email’ => ‘<removed>’,
‘payer_id’ => ‘9G5554813M769074G’,
‘payer_status’ => ‘verified’,
‘payment_date’ => ‘2015-11-19 15:34:56’,
‘payment_fee’ => ‘0.01’,
‘payment_gross’ => ‘0.01’,
‘payment_status’ => ‘Completed’,
‘payment_type’ => ‘instant’,
‘protection_eligibility’ => ‘Ineligible’,
‘quantity1’ => ‘1’,
‘receiver_email’ => ‘<removed>’,
‘receiver_id’ => ‘9G5554813M769074G’,
‘resend’ => ‘false’,
‘residence_country’ => ‘US’,
‘tax’ => ‘0.00’,
‘tax1’ => ‘0.00’,
‘transaction_subject’ => ”,
‘txn_id’ => ‘9G5554813M769074G’,
‘txn_type’ => ‘subscr_signup’,
‘verify_sign’ => ‘9G5554813M769074G’,
‘proxy_verified’ => ‘JVzoo’,
‘s2member_log’ =>
array (
0 => ‘IPN received on: Thu Nov 19, 2015 8:35:29 pm UTC’,
1 => ‘s2Member POST vars verified with a Proxy Key’,
2 => ‘s2Member originating domain ($_SERVER["HTTP_HOST"]) validated.’,
3 => ‘s2Member txn_type identified as ( web_accept|subscr_signup ).’,
4 => ‘s2Member txn_type identified as ( web_accept|subscr_signup ) w/o update vars.’,
5 => ‘Signup Confirmation Email sent to: “<removed>” <<removed>>.’,
6 => ‘Storing IPN signup vars into a Transient Queue. These will be processed on registration.’,
),
‘subscr_gateway’ => ‘JVzoo’,
‘subscr_id’ => ‘9G5554813M769074G’,
‘subscr_baid’ => ‘9G5554813M769074G’,
‘subscr_cid’ => ‘9G5554813M769074G’,
‘eotper’ => NULL,
‘ccaps’ => NULL,
‘level’ => ‘1’,
‘ip’ => ”,
‘period1’ => ‘0 D’,
‘mc_amount1’ => ‘0.00’,
‘initial_term’ => ‘0 D’,
‘initial’ => NULL,
‘regular’ => NULL,
‘regular_term’ => NULL,
‘recurring’ => ‘0’,
‘currency’ => ‘USD’,
‘currency_symbol’ => ‘$’,
‘s2member_paypal_proxy’ => ‘JVzoo’,
‘s2member_paypal_proxy_verification’ => ‘fe376224669a201477d269df8e713d5b’,
)

https://wordpress.org/plugins/s2member/