threadKey property
Input for creating or updating a thread.
Otherwise, output only. ID for the thread. Supports up to 4000 characters.
This ID is unique to the Chat app that sets it. For example, if multiple
Chat apps create a message using the same thread key, the messages are
posted in different threads. To reply in a thread created by a person or
another Chat app, specify the thread name
field instead.
Optional.
Implementation
core.String? threadKey;