Original comment by @spinscale:

From: https://discuss.elastic.co/t/make-message-text-not-required-for-slack-action/120939

The Slack action currently requires message.text to be present, though slack will gladly require a message without it, as a message can have an attachment which contains the text to be displayed. The current requirement for message.text means a message with attachment needs both message.text and message.attachments.text, causing the message displayed in Slack to look slightly disjointed. Would be excellent to remove this requirement.