I understand it’s a warning, but imagine it could be fatal in 8.6 which is going to be out in November.
2026/11/03 20:11:56 [error] 361360#361360: *80 FastCGI sent in stderr: “PHP message: PHP Warning: Undefined array key “x_subscription_id” in /path/to/mydomain.com/public_html/wp-content/plugins/s2member-pro/src/includes/classes/gateways/authnet/authnet-notify-in.inc.php on line 70; PHP message: PHP Warning: Undefined array key “x_subscription_id” in /path/to/mydomain.com/public_html/wp-content/plugins/s2member-pro/src/includes/classes/gateways/authnet/authnet-notify-in.inc.php on line 122” while reading response header from upstream, client: 1.1.1.1., server: mydomain.com, request: “POST /?s2member_pro_authnet_notify=1 HTTP/1.1”, upstream: “fastcgi://unix:/var/run/php/php8.5-fpm.sock:”, host: “mydomain.com”