Hi Albert,
Like Robert has mentioned, this should get passed through from the trigger, but I believe you have to define it as a condition. We have been able to successfully pass it through in our workflows. Here's an example of one of our triggers:

If you then add Flow.conversationId as a variable to your workflow (under Resources - Data) and set it to "Input to flow", it should get passed through.
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James Foster
Connect Managed Services (UK) Limited
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