For mention posts like @channel or @everyone from Slack bot, writing them as-is won’t work properly, so you need to use special notation.

Success example: Use notation

Via Slack bot, if you use notation like this:

' Hello! Project'

It seems to be properly recognized as a mention as shown below.

Failure example: Writing @channel directly

With the same feeling as posting from the Slack app normally,

'@channel Hello! Project'

even if you write it like this, it doesn’t seem to be properly recognized as a mention via Slack bot as shown below.

Official Slack Information

This was also mentioned in Slack Help Center Bot messages.

Bot messages

If you wish to trigger one of these notifications with a bot message, the message should contain <!channel> or <!everyone>.

I hope this helps those who were wondering “I made a Slack bot but can’t make mention posts…”

That’s all from the Gemba.