To update the content of a Slack notification previously sent via Courier, you need to set the "replacement key" path in the Slack channel settings within your notification template.
We typically use "ts" as the value. Courier will then look for this key in the data block you pass to our API and use that to update an existing message instead of posting a new one.
Setting the Replacement Key Path in the Slack Channel Settings
Open the notification
Hover over the Slack Channel (or Direct Message channel with Slack set as the integration)
Click on the Channel Settings slide out menu
4. Click to open the Slack integration
5. Set the Replacement Key Path
