NiFi PutSlack Proxy error

[#1]

Hi, I am using putSlack in NiFi 1.26.0. Where i have configured following:

• Webhook URL
• Webhook text
• Channel
• SSL Context service which has slack cert. (JKS)

Getting below error while running the putSlack in DEV server.

"failed to open connection. [java.net.unknownhosexception: hooks.slack.com]

Could any one please help to fix this.