Gitlab webhook to Slack didn't work suddenly

Hi all,

I’ve setup my gitlab webhook to Slack previously it was working fine, but it suddenly just not working, means no notificattion is being sent to Slack.

I tried to use curl command to test the webhook, it works fine, but it just didn’t work from gitlab GUI. My webhook URL is

I tried to run “gitlab-ctl tail” and it shows something like OpenSSL error, SSL verification failed.
Any suggestion on the troubleshooting?

Thank you.
Best regards,