How can I be notified when a customer replies to a message?

Summary:

Hi,

Employee posts a message → assigned HR Help Desk agent receives a Bell notification → recipient/message controlled from Notification Preferences.

I followed below steps still I cannot see the notification preferences showing this trigger after configured in Sandbox and after publish preference is not showing the trigger

Trigger Type = Before Insert

Application Composer
→ Standard Objects
→ HR Help Desk Request
→ Messages
→ Server Scripts
→ Triggers

Link: How can I be notified when a customer replies to a message?

Please suggest

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