systemd: failed to add systemd socket

[scifinder]

Hello!
I want to use systemd. I do everything according to this instruction. My OS is Debian, so files are placed along these paths: /etc/systemd/system/openswoole.socket and /etc/systemd/system/openswoole.service. On run sudo systemctl start openswoole.socket I get an error:

[2024-02-08 22:59:50 @2706.0]   WARNING Server::add_systemd_socket(): invalid LISTEN_PID
PHP Fatal error:  OpenSwoole\Server::__construct(): failed to add systemd socket in /var/www/openswoole/server.php on line 2

Tell me, what could be the reason?