BroadcastContentFormat

content is a serialised Tiptap document.

content is a JSON array of Slack Block Kit blocks, as sent to chat.postMessage. Every block type Slack accepts is allowed, including ones the Plain composer cannot author.

Three things to know:

• Interactive elements do not work. A button without a url, a select, a datepicker or an input block will render in Slack and do nothing when used, because a broadcast has no app listening for the interaction payload. Use buttons with a url.
• Images must be publicly reachable. Slack fetches image_url itself, and a Block Kit broadcast has no Plain workspace files behind it.
• A broadcast is one Slack message, so it is subject to Slack's block limit and to Plain's own payload budget. Oversized content is rejected when it is written.

Content is checked against Slack's own Block Kit schema as it is written, so a malformed block is normally a mutation error rather than a failed send. That check needs the workspaceSlackIntegration:read permission and a connected Slack workspace: an API key without it still works, but its content is only checked when the broadcast is sent.

Content in this format cannot be edited in the Plain app.