If you want to track the Salesforce Send Conversation Messages invocations, then query ConvMessageSendRequest object/entity.

Whenever Send Conversation Messages action is invoked, it is logged in ConvMessageSendRequest object/entity.

Sample SOQL:

SELECT Id, CreatedDate, CompletedDate, RequestStatus, TotalMessageCount,
SuccessMessageCount, SuccessMessageIdentifiers,
FailedMessageCount, FailedMessageErrorReasons, FailedMessageIdentifiers,
InProgressMessageCount, InProgressMessageIdentifiers,
PendingMessageCount, PendingMessageIdentifiers
FROM ConvMessageSendRequest

https://developer.salesforce.com/docs/atlas.en-us.object_reference.meta/object_reference/sforce_api_objects_convmessagesendrequest.htm