Where do I enter ‘Deny Reason’ [denyreason]

Hello,
beautiful plugin.
However, I need help figuring out where do I enter ‘Deny reason’ text when rejecting a booking? I tried multiple scenarios, back and front, hoping it would have to do with the little speech bubble (‘Edit Note’) icon next to a booking entry in the panel with the booking listing, but seems like this speech bubble Note serves exclusively as internal note for the admin, nothing else.

Please help me figure out where to enter the information that gets rendered in the notification email via [denyreason] shortcode.