As Slack plans to deprecate webhook support, Updating incoming webhooks from new Slack apps with the Jira Automation "Send Slack message" action, the "Channel or user" field does not work as expected.

Workaround:

Instead of using the built-in "Send Slack notification" action, use the "Send web request" action with Slack's
chat.postMessage API:

1 Create a Slack App at https://api.slack.com/apps
2 Add the chat:write Bot Token Scope under OAuth & Permissions
3 Install the app to your workspace and copy the Bot User OAuth Token (xoxb-...)
4 In your A4J rule, replace the "Send Slack notification" action with "Send web request":

• URL: [*https://slack.com/api/chat.postMessage*]

• Method: POST

• Headers: Add Authorization with the value Bearer xoxb-your-token. You can enter this as a plain text value or

   *   use the *secret value option to keep the token masked and secure — both approaches work, but the secret option is
   **   recommended.

• Content-Type header: application/json; charset=utf-8

• Body: {"channel": "CHANNEL_ID", "text": "Your message with issue.key smart values"}

This approach fully restores channel override functionality since chat.postMessage respects the channel field, unlike
the new incoming webhooks. You can target any channel (by ID) or even send DMs to users (by Slack User ID).