If you want to mention someone in notifications sent to Slack, you can do so by configuring Slack's notification settings.
Please note that Slack notifications are only supported for the template URL.
Receive mention notifications using Slack's keyword search feature
By setting up email addresses as keywords in Slack's keyword notification feature, you can receive notifications for events in Spir with the participants' email addresses included along with the schedule. Notifications for events involving the specified email addresses can then be received as mentions. Please be aware that the keyword notification feature needs to be set up individually.
For instructions on how to set up keyword notifications, please refer to the following article within Slack: "Add your own custom keywords".
https://slack.com/resources/using-slack/customize-your-notifications-in-slack