site: https://www.proteawines.jp/shop/
OS: Debian 11.0 (64-bit)
Zencart: 1.5.6c with customizations for Japanese language
DB: MariaDB 10.3.24
PHP (with nginx/php-fpm): 7.3.15-3

Paypal send notifications of updates to IPN IP addresses in December 2020, which I ignored since I have no restrictions in my route, OS firewall or nginx web server configuration for HTTPS traffic.

Paypal has been working for transactions, last one was yesterday 22nd May (I could capture the payment successfully in ZenCart, and it is listed in my PayPal account correctly as "pending").

That said, the morning I received a message from Paypal stating that there are IPN errors, and that IPN may be stopped if this continues.

Dear Gernot Hassenpflug,

Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:

https://www.proteawines.jp/shop/ipn_main_handler.php

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.

Thank you for your prompt attention to this issue.

PROTECT YOUR PASSWORD

NEVER give your password to anyone, including PayPal employees. Protect yourself against fraudulent websites by opening a new web browser (e.g. Internet Explorer or Firefox) and typing in the PayPal URL every time you log in to your account.

Not sure why you received this email? Learn more [https://www.paypal.com/jp/smarthelp/...4.0&xt=104038]

PayPal Pte. Ltd. is a Singaporean company registered with the Financial Services Agency of Japan as a (1) Funds Transfer Business Operator with Registration No. 00026 issued by the Director-General of the Kanto Local Finance Bureau and (2) Third Party-type Issuer of Prepaid Payment Instruments with Registration No. 00705 issued by the Director-General of the Kanto Local Finance Bureau.

PayPal RT000111:en_US(en-JP):1.0.0:a5c4c469241f6
I checked as best I could the Paypal module code, there is no explicit listings of IP addresses.
In the ZenCart error logs there are errors of this form:

[23-May-2021 12:39:49 Asia/Tokyo] Request URI: /shop/ipn_main_handler.php, IP address: 173.0.81.65
#1 trigger_error() called at [/<snipped>/includes/classes/db/mysql/query_factory.php:171]
#2 queryFactory->show_error() called at [/<snipped>/includes/classes/db/mysql/query_factory.php:143]
#3 queryFactory->set_error() called at [/<snipped>/includes/classes/db/mysql/query_factory.php:270]
#4 queryFactory->Execute() called at [/<snipped>/includes/functions/functions_general.php:952]
#5 zen_db_perform() called at [/<snipped>/ipn_main_handler.php:439]
--> PHP Fatal error: 1366:Incorrect integer value: '' for column `zencartshop`.`paypal_payment_status_history`.`paypal_ipn_id` at row 1 :: INSERT INTO paypal_payment_status_history (paypal_ipn_id, txn_id, parent_txn_id, payment_status, pending_reason, date_added) VALUES ('', '5****************', '1****************', 'Completed', '', now()) ==> (as called by) /<snipped>/includes/functions/functions_general.php on line 952 <== in /<snipped>/includes/classes/db/mysql/query_factory.php on line 171.
(DB values replaced by asterisks, paths snipped)

Not sure if there is anything I need to do regarding IPN IP addresses, or whether the error is caused by, say, strict mode in the DB?

Any comments appreciated.