Clarify about chat.update only work with channels and not DMs

[nahuelhds]

Hi! Was trying the example for updating a message and two things that happened.

The action succeed but no update happen. First of all, the action itself was failing, actually with message_not_found error but the action reports success anyway.

See the following image

You can see the last three lines

##[debug]Set output response = {"ok":false,"error":"message_not_found","response_metadata":{"scopes":["incoming-webhook","chat:write"],"acceptedScopes":["chat:write"]}}
##[debug]Set output time = 1738447171
##[debug]Finishing: Update the original message with success

Ok = False, but "Update the original message with sucess" (?

Doing some more research, I learned that my issue was that I was trying to post to a private message and this only works with channels. I'd be nice to warn about this in the docs :)

[zimeg]

Hey @nahuelhds 👋 Thanks for sharing the details of your investigation into this! 🔍

The failure mode of this action defaults to silent API errors which can be toggled on to cause errors from the Slack API to exit the step with an error:

  - uses: slackapi/[email protected]
    with:
+     errors: true

This can certainly create confusing cases like what you're finding, but this default was picked to avoid breaking an entire CI pipeline if, perhaps, posting a "completion" message was to fail as the very last step due to a server outage or similar.

Updating a message using a user ID with chat.update also isn't supported, as you've noted. I agree this isn't a nice edge to discover... However, the conversation ID of the DM can be used here instead! This will start with a "D":

  - uses: slackapi/[email protected]
    with:
      method: chat.update
      token: ${{ secrets.SLACK_BOT_TOKEN }}
      payload: |
+       channel: D0123456789
        ts: "${{ steps.launch_sequence.outputs.ts }}"
        text: "Deployment finished! :rocket:"

Setting errors to true might be helpful when debugging, but I'm hoping the updated conversation ID helps with these message updates - please let me know in whichever case or if other questions arise 🙏 ✨

I'll share a note about the allowed conversation types with our documentation team since I'm hoping the Slack API reference can serve as a source of truth for accepted arguments 📚