If you received the following error message in response to this Slack action in your workflow, this article can help you troubleshoot possible causes:
"Why it failed:
This action may have failed for one of the following reasons: User has been disabled or does not exist, channel has been archived or does not exist, Message is too long, Message includes too many attachments, rate limit exceeded.
Please check if: (1) The user is active, (2) channel is active, (3) message includes fewer than 4000 characters, (4) message includes fewer than 100 attachments, (5) daily rate limit has not been exceeded."
In this case, the action in your workflow may have failed for one of following reasons: the channel in question may not exist, the user addressed in your message may not exist, the message is too long or includes too many attachments, or your domain's daily rate limit has been exceeded. For troubleshooting each of these items, please read on below.
Channel is Active
To confirm that the noted channel is active in your Slack team, please navigate into your Slack instance. Locate the channel among your list in the left navigation bar, or click on the "Channel" header to browse and search for it.
If you cannot find your channel, it may not exist or has since been archived or deleted. Archived or deleted channels cannot be restored to an active state.
User is Active
To confirm that any user noted in your message is active, please navigate into your Slack instance. You can search for active users by name or username in the search bar in the top right corner:
If the user is not currently active in your Slack team, they must be invited and create an account before messages can be sent to them. See here for more information.
Message Meets Limits
Please ensure that your message is within the limits that Slack sets for length and attachments: Slack messages can be up to 4000 characters long, and contain no more than 100 attachments.
Rate Limit Exceeded
Slack teams are subject to daily rate limits, which control the flow of team data to ensure that Slack's system is not overwhelmed. If your team reaches this limit, no further messages will be able to be sent for that day. In this case, the only real solution would be to wait roughly 24 hours for the limit to be removed, before trying to send your message again.
If you need assistance confirming that your team has reached its daily rate limit, please contact Support.