Hi @Kevmcdonk ,
How is your flow created? Please show me a screenshot.
Message posted as a bot to a Teams channel can contain @mentions of other users. To create an @mention you need to surround their email address or user ID with the <at> tag.
Hello <at>email@example.com</at> - your request has been completed!
I have made a test likes below, which is working properly to post message with @mention.
Further, the following blog for your reference:
The best way for this to occur is for MS to build into the Post your own adaptive card as the Flow bot to a channel to actually contain an advanced option such as Summary and IsAlert which is available on the Post your own adaptive card as the Flow bot to a user connector. Until MS builds it, it'll be next to impossible 😞
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