Mule Processing Strategies - Calling an Asynchronous Private Stream from a Synchronous Stream

Question

I am trying to call a private async stream from a main synchronous stream, for example:

<flow name="main" doc:name="main" processingStrategy="synchronous">
    <poll frequency="10000">
        <set-payload value="main"></set-payload>
    </poll>

    <flow-ref name="async-private" />
    <flow-ref name="private" />

</flow>
<flow name="private" processingStrategy="synchronous">
    <logger level="ERROR" message="sync" />
</flow>

<flow name="async-private" processingStrategy="asynchronous">
    <logger level="ERROR" message="async" />
</flow>

But this does not work and leads to the following exception:

Unable to handle synchronous event asynchronously. The message payload is of type: String (org.mule.api.MessagingException)

What's going on here?

UPDATE

It works if I exchange async-ref-ref in tags <async>. But why do I need this? This is mistake?

Answer 1

This is a function.

. . , . , Mule <async>.