apache起動エラー(httpd.service: Failed with result 'protocol')について

Centos9にApacheをインストールしています。

systemctl start httpd
を実行したところ、以下のエラーとなります。

Job for httpd.service failed because the service did not take the steps required by its unit configuration.
See "systemctl status httpd.service" and "journalctl -xe" for details.

systemctl status httpd
を実行したところ以下のとおり確認できます。

● httpd.service - The Apache HTTP Server
Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
Drop-In: /usr/lib/systemd/system/httpd.service.d
mqphp-fpm.conf
Active: failed (Result: protocol)
Docs: man:httpd.service(8)
Process: 86045 ExecReload=/usr/sbin/httpd $OPTIONS -k graceful (code=exited, status=0/SUCCESS)
Process: 89240 ExecStart=/usr/sbin/httpd $OPTIONS -DFOREGROUND (code=exited, status=0/SUCCESS)
Main PID: 89240 (code=exited, status=0/SUCCESS)
Status: "Reading configuration..."

systemd[1]: Starting The Apache HTTP Server...
httpd[89240]: httpd (pid 88319) already running
systemd[1]: httpd.service: Failed with result 'protocol'.
systemd[1]: Failed to start The Apache HTTP Server.

原因と対処方法がわからず困っております。
ご教示頂けませんでしょうか。