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Use a Slack webhook to create a contact point in slack.
Follow the link below to create a slack webhook and get its url- https://api.slack.com/messaging/webhooks
One the webhook is created, enter its URL in the webhook field while creating the contact point.
Optionally, you can use the optional settings Use the Optional Slack Settings to mention specific user/group or send alerts to entire channel.
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Setting webhook contact point integration
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