Slack triggers fail to deliver webhooks when messages contain attachments | ComposioHQ | Page 1

Description:

Slack message triggers are not firing webhooks when messages contain attachments. The trigger works correctly for text-only messages but silently fails when attachments are present. This is for the SLACK toolkit (not the SLACKBOT toolkit).

Reproduction Steps:

Set up a Slack trigger (e.g., SLACK_RECEIVE_MESSAGE or "New Message Received")
Configure webhook endpoint
Send test messages to the monitored channel:
Test A: Text only → ✅ Webhook delivered
Test B: Text + attachment (image/file) → ❌ No webhook
Test C: Attachment only (no text) → ❌ No webhook

Expected Behavior:

Webhook should be delivered for all message types, with the full Slack event payload including any attachments or filesarrays.

Actual Behavior:

Webhook is only delivered for text-only messages. Messages containing attachments are silently dropped—no webhook is sent and no error appears.

Environment:

Toolkit: slack
Trigger type: SLACK_RECEIVE_MESSAGE
Trigger ID: ti_6V3ZSSQkg_tW
CONNECTION ID: ca_XCtlUyFoQy5_

Impact:

This blocks use cases where AI agents need to process images, documents, or other files shared in Slack (e.g., analyzing screenshots, processing PDFs, extracting data from shared files).

Additional Context:

No errors visible in the trigger logs dashboard. The issue appears to be in Composio's event processing layer, possibly filtering or failing to parse messages with the files or attachments field present. I can't even see the log of the event in the Composio Logs dashboard.

I uninstalled the Composio Slack app, deleted the connection and everything, then installed everything again. Still same issue.

Please provide a fix ASAP, happy to help if need be or if you have any questions.
Best,

Maybe could be due to the fact that your backend tries to get the attachements, but you need to be authenticated to get them. So it fails.

#Slack triggers fail to deliver webhooks when messages contain attachments