In the chatterBody text template, we can’t find a mention for the contact’s owner. (Hint: Mentions use this format: @[{!globalVariable.field_API_Name}].)

Hi @Bola Thanuja,  

Update your chatterBody text template to include the exact mention syntax: @[{!$Record.OwnerId}]

Key steps to fix it:

1. Open your chatterBody Text Template in the Flow toolbox.
2. Change the template dropdown from "View as Rich Text" to View as Plain Text. (Rich Text can sometimes add hidden HTML tags that break the Trailhead checker).
3. Type the mention syntax exactly as @[{!$Record.OwnerId}]. Because you are in a Schedule-Triggered Flow running on the Contact object, $Record is the global variable that represents the current Contact in the batch.